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 $94.74   10.232%   $104.4338   $104.43   $104.45   $104.40  
  Purchase #2 $151.81   10.145%   $167.2111   $167.21   $167.20   $167.20  
  Purchase #3 $112.67   12.582%   $126.8461   $126.85   $126.85   $126.80  
  Purchase #4 $27.84   12.399%   $31.2919   $31.29   $31.30   $31.30  
  Purchase #5 $167.37   9.627%   $183.4827   $183.48   $183.50   $183.50  
  Purchase #6 $225.56   9.433%   $246.8371   $246.84   $246.85   $246.80  
  Purchase #7 $34.39   4.825%   $36.0493   $36.05   $36.05   $36.00  
  7 purchase totals = $814.38       $896.1520   $896.15   $896.20   $896.00