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 $226.98   10.757%   $251.3962   $251.40   $251.40   $251.40  
  Purchase #2 $231.39   8.527%   $251.1206   $251.12   $251.10   $251.10  
  Purchase #3 $54.94   6.640%   $58.588   $58.59   $58.60   $58.60  
  Purchase #4 $235.58   12.697%   $265.4916   $265.49   $265.50   $265.50  
  Purchase #5 $99.94   8.822%   $108.7567   $108.76   $108.75   $108.80  
  Purchase #6 $116.43   10.166%   $128.2663   $128.27   $128.25   $128.30  
  Purchase #7 $181.34   5.507%   $191.3264   $191.33   $191.35   $191.30  
  7 purchase totals = $1,146.60       $1,254.9458   $1,254.96   $1,254.95   $1,255.00