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 $243.47   9.237%   $265.9593   $265.96   $265.95   $266.00  
  Purchase #2 $234.81   13.560%   $266.6502   $266.65   $266.65   $266.70  
  Purchase #3 $121.41   12.616%   $136.7271   $136.73   $136.75   $136.70  
  Purchase #4 $243.81   9.498%   $266.9671   $266.97   $266.95   $267.00  
  Purchase #5 $94.44   7.340%   $101.3719   $101.37   $101.35   $101.40  
  Purchase #6 $106.87   3.521%   $110.6329   $110.63   $110.65   $110.60  
  Purchase #7 $11.86   7.317%   $12.7278   $12.73   $12.75   $12.70  
  7 purchase totals = $1,056.67       $1,161.0363   $1,161.04   $1,161.05   $1,161.10