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 $232.84   11.788%   $260.2872   $260.29   $260.30   $260.30  
  Purchase #2 $147.26   13.505%   $167.1475   $167.15   $167.15   $167.10  
  Purchase #3 $95.33   11.265%   $106.0689   $106.07   $106.05   $106.10  
  Purchase #4 $74.76   6.313%   $79.4796   $79.48   $79.50   $79.50  
  Purchase #5 $165.97   8.430%   $179.9613   $179.96   $179.95   $180.00  
  Purchase #6 $147.71   13.549%   $167.7232   $167.72   $167.70   $167.70  
  Purchase #7 $61.32   5.772%   $64.8594   $64.86   $64.85   $64.90  
  7 purchase totals = $925.19       $1,025.5271   $1,025.53   $1,025.50   $1,025.60