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 $201.57   13.135%   $228.0462   $228.05   $228.05   $228.00  
  Purchase #2 $12.62   10.200%   $13.9072   $13.91   $13.90   $13.90  
  Purchase #3 $196.33   10.215%   $216.3851   $216.39   $216.40   $216.40  
  Purchase #4 $24.65   5.626%   $26.0368   $26.04   $26.05   $26.00  
  Purchase #5 $179.78   8.130%   $194.3961   $194.40   $194.40   $194.40  
  Purchase #6 $54.92   10.778%   $60.8393   $60.84   $60.85   $60.80  
  Purchase #7 $110.53   7.677%   $119.0154   $119.02   $119.00   $119.00  
  7 purchase totals = $780.40       $858.6261   $858.65   $858.65   $858.50