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 $121.58   3.692%   $126.0687   $126.07   $126.05   $126.10  
  Purchase #2 $58.71   3.650%   $60.8529   $60.85   $60.85   $60.90  
  Purchase #3 $182.42   10.852%   $202.2162   $202.22   $202.20   $202.20  
  Purchase #4 $81.74   4.439%   $85.3684   $85.37   $85.35   $85.40  
  Purchase #5 $179.67   8.118%   $194.2556   $194.26   $194.25   $194.30  
  Purchase #6 $45.70   7.605%   $49.1755   $49.18   $49.20   $49.20  
  Purchase #7 $209.30   12.831%   $236.1553   $236.16   $236.15   $236.20  
  7 purchase totals = $879.12       $954.0926   $954.11   $954.05   $954.30