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 $188.76   7.533%   $202.9793   $202.98   $203.00   $203.00  
  Purchase #2 $91.34   4.298%   $95.2658   $95.27   $95.25   $95.30  
  Purchase #3 $87.80   5.406%   $92.5465   $92.55   $92.55   $92.50  
  Purchase #4 $33.55   11.820%   $37.5156   $37.52   $37.50   $37.50  
  Purchase #5 $98.48   6.387%   $104.7699   $104.77   $104.75   $104.80  
  Purchase #6 $162.29   3.365%   $167.7511   $167.75   $167.75   $167.80  
  Purchase #7 $201.97   6.620%   $215.3404   $215.34   $215.35   $215.30  
  7 purchase totals = $864.19       $916.1686   $916.18   $916.15   $916.20