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 $56.82   5.827%   $60.1309   $60.13   $60.15   $60.10  
  Purchase #2 $151.58   7.494%   $162.9394   $162.94   $162.95   $162.90  
  Purchase #3 $21.36   13.314%   $24.2039   $24.20   $24.20   $24.20  
  Purchase #4 $22.73   12.708%   $25.6185   $25.62   $25.60   $25.60  
  Purchase #5 $219.32   4.469%   $229.1214   $229.12   $229.10   $229.10  
  Purchase #6 $190.90   5.648%   $201.682   $201.68   $201.70   $201.70  
  Purchase #7 $160.52   4.398%   $167.5797   $167.58   $167.60   $167.60  
  7 purchase totals = $823.23       $871.2758   $871.27   $871.30   $871.20