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 $52.86   4.112%   $55.0336   $55.03   $55.05   $55.00  
  Purchase #2 $194.76   5.715%   $205.8905   $205.89   $205.90   $205.90  
  Purchase #3 $250.59   4.681%   $262.3201   $262.32   $262.30   $262.30  
  Purchase #4 $110.62   5.617%   $116.8335   $116.83   $116.85   $116.80  
  Purchase #5 $185.79   13.515%   $210.8995   $210.90   $210.90   $210.90  
  Purchase #6 $23.56   5.407%   $24.8339   $24.83   $24.85   $24.80  
  Purchase #7 $207.66   12.224%   $233.0444   $233.04   $233.05   $233.00  
  7 purchase totals = $1,025.84       $1,108.8555   $1,108.84   $1,108.90   $1,108.70