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 $154.64   6.118%   $164.1009   $164.10   $164.10   $164.10  
  Purchase #2 $70.62   9.308%   $77.1933   $77.19   $77.20   $77.20  
  Purchase #3 $10.77   6.664%   $11.4877   $11.49   $11.50   $11.50  
  Purchase #4 $84.47   3.671%   $87.5709   $87.57   $87.55   $87.60  
  Purchase #5 $95.41   9.216%   $104.203   $104.20   $104.20   $104.20  
  Purchase #6 $226.72   8.858%   $246.8029   $246.80   $246.80   $246.80  
  Purchase #7 $230.80   4.306%   $240.7382   $240.74   $240.75   $240.70  
  7 purchase totals = $873.43       $932.0969   $932.09   $932.10   $932.10