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 $239.97   11.525%   $267.6265   $267.63   $267.65   $267.60  
  Purchase #2 $229.52   7.835%   $247.5029   $247.50   $247.50   $247.50  
  Purchase #3 $159.34   7.165%   $170.7567   $170.76   $170.75   $170.80  
  Purchase #4 $153.68   7.520%   $165.2367   $165.24   $165.25   $165.20  
  Purchase #5 $143.75   11.819%   $160.7398   $160.74   $160.75   $160.70  
  Purchase #6 $60.56   10.576%   $66.9648   $66.96   $66.95   $67.00  
  Purchase #7 $232.37   12.825%   $262.1715   $262.17   $262.15   $262.20  
  7 purchase totals = $1,219.19       $1,340.9989   $1,341.00   $1,341.00   $1,341.00