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 $156.98   3.323%   $162.1964   $162.20   $162.20   $162.20  
  Purchase #2 $219.94   7.571%   $236.5917   $236.59   $236.60   $236.60  
  Purchase #3 $66.25   4.221%   $69.0464   $69.05   $69.05   $69.00  
  Purchase #4 $71.29   11.392%   $79.4114   $79.41   $79.40   $79.40  
  Purchase #5 $163.65   3.457%   $169.3074   $169.31   $169.30   $169.30  
  Purchase #6 $156.37   11.165%   $173.8287   $173.83   $173.85   $173.80  
  Purchase #7 $49.76   9.644%   $54.5589   $54.56   $54.55   $54.60  
  7 purchase totals = $884.24       $944.9409   $944.95   $944.95   $944.90