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 $170.51   9.464%   $186.6471   $186.65   $186.65   $186.60  
  Purchase #2 $99.68   11.186%   $110.8302   $110.83   $110.85   $110.80  
  Purchase #3 $11.39   9.691%   $12.4938   $12.49   $12.50   $12.50  
  Purchase #4 $138.43   7.748%   $149.1556   $149.16   $149.15   $149.20  
  Purchase #5 $212.74   5.459%   $224.3535   $224.35   $224.35   $224.40  
  Purchase #6 $167.77   3.295%   $173.298   $173.30   $173.30   $173.30  
  Purchase #7 $77.65   8.776%   $84.4646   $84.46   $84.45   $84.50  
  7 purchase totals = $878.17       $941.2428   $941.24   $941.25   $941.30