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 $188.66   8.814%   $205.2885   $205.29   $205.30   $205.30  
  Purchase #2 $63.96   5.363%   $67.3902   $67.39   $67.40   $67.40  
  Purchase #3 $97.94   7.322%   $105.1112   $105.11   $105.10   $105.10  
  Purchase #4 $171.35   3.571%   $177.4689   $177.47   $177.45   $177.50  
  Purchase #5 $195.68   4.722%   $204.92   $204.92   $204.90   $204.90  
  Purchase #6 $37.70   12.599%   $42.4498   $42.45   $42.45   $42.40  
  Purchase #7 $222.43   5.826%   $235.3888   $235.39   $235.40   $235.40  
  7 purchase totals = $977.72       $1,038.0174   $1,038.02   $1,038.00   $1,038.00