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 $82.53   10.534%   $91.2237   $91.22   $91.20   $91.20  
  Purchase #2 $65.67   9.492%   $71.9034   $71.90   $71.90   $71.90  
  Purchase #3 $118.77   11.412%   $132.324   $132.32   $132.30   $132.30  
  Purchase #4 $245.68   10.815%   $272.2503   $272.25   $272.25   $272.30  
  Purchase #5 $41.74   6.410%   $44.4155   $44.42   $44.40   $44.40  
  Purchase #6 $26.91   8.479%   $29.1917   $29.19   $29.20   $29.20  
  Purchase #7 $182.53   6.644%   $194.6573   $194.66   $194.65   $194.70  
  7 purchase totals = $763.83       $835.9659   $835.96   $835.90   $836.00