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 $188.26   7.281%   $201.9672   $201.97   $201.95   $202.00  
  Purchase #2 $92.93   12.393%   $104.4468   $104.45   $104.45   $104.40  
  Purchase #3 $81.56   12.617%   $91.8504   $91.85   $91.85   $91.90  
  Purchase #4 $190.92   9.564%   $209.1796   $209.18   $209.20   $209.20  
  Purchase #5 $248.65   5.503%   $262.3332   $262.33   $262.35   $262.30  
  Purchase #6 $60.39   5.317%   $63.6009   $63.60   $63.60   $63.60  
  Purchase #7 $89.74   9.234%   $98.0266   $98.03   $98.05   $98.00  
  7 purchase totals = $952.45       $1,031.4047   $1,031.41   $1,031.45   $1,031.40