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 $202.37   8.715%   $220.0065   $220.01   $220.00   $220.00  
  Purchase #2 $50.92   11.303%   $56.6755   $56.68   $56.70   $56.70  
  Purchase #3 $190.51   11.429%   $212.2834   $212.28   $212.30   $212.30  
  Purchase #4 $187.62   9.434%   $205.3201   $205.32   $205.30   $205.30  
  Purchase #5 $46.45   8.400%   $50.3518   $50.35   $50.35   $50.40  
  Purchase #6 $216.28   11.124%   $240.339   $240.34   $240.35   $240.30  
  Purchase #7 $64.43   11.129%   $71.6004   $71.60   $71.60   $71.60  
  7 purchase totals = $958.58       $1,056.5767   $1,056.58   $1,056.60   $1,056.60