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 $60.45   7.234%   $64.823   $64.82   $64.80   $64.80  
  Purchase #2 $235.58   5.401%   $248.3037   $248.30   $248.30   $248.30  
  Purchase #3 $127.92   12.137%   $143.4457   $143.45   $143.45   $143.40  
  Purchase #4 $182.98   12.732%   $206.277   $206.28   $206.30   $206.30  
  Purchase #5 $158.36   7.802%   $170.7152   $170.72   $170.70   $170.70  
  Purchase #6 $124.89   12.314%   $140.269   $140.27   $140.25   $140.30  
  Purchase #7 $39.86   3.654%   $41.3165   $41.32   $41.30   $41.30  
  7 purchase totals = $930.04       $1,015.1501   $1,015.16   $1,015.10   $1,015.10