Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $226.92   12.201%   $254.6065   $254.61   $254.60   $254.60  
  Purchase #2 $236.47   12.222%   $265.3714   $265.37   $265.35   $265.40  
  Purchase #3 $181.39   12.388%   $203.8606   $203.86   $203.85   $203.90  
  Purchase #4 $118.42   7.658%   $127.4886   $127.49   $127.50   $127.50  
  Purchase #5 $198.42   7.256%   $212.8174   $212.82   $212.80   $212.80  
  Purchase #6 $24.41   6.387%   $25.9691   $25.97   $25.95   $26.00  
  Purchase #7 $205.33   10.216%   $226.3065   $226.31   $226.30   $226.30  
  7 purchase totals = $1,191.36       $1,316.4201   $1,316.43   $1,316.35   $1,316.50