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 $246.39   4.297%   $256.9774   $256.98   $257.00   $257.00  
  Purchase #2 $147.79   10.272%   $162.971   $162.97   $162.95   $163.00  
  Purchase #3 $207.81   4.647%   $217.4669   $217.47   $217.45   $217.50  
  Purchase #4 $24.51   4.814%   $25.6899   $25.69   $25.70   $25.70  
  Purchase #5 $152.97   9.364%   $167.2941   $167.29   $167.30   $167.30  
  Purchase #6 $46.39   4.376%   $48.42   $48.42   $48.40   $48.40  
  Purchase #7 $206.75   13.576%   $234.8184   $234.82   $234.80   $234.80  
  7 purchase totals = $1,032.61       $1,113.6377   $1,113.64   $1,113.60   $1,113.70