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 $241.97   9.619%   $265.2451   $265.25   $265.25   $265.20  
  Purchase #2 $67.65   5.236%   $71.1922   $71.19   $71.20   $71.20  
  Purchase #3 $185.66   6.462%   $197.6573   $197.66   $197.65   $197.70  
  Purchase #4 $198.32   6.281%   $210.7765   $210.78   $210.80   $210.80  
  Purchase #5 $60.39   4.455%   $63.0804   $63.08   $63.10   $63.10  
  Purchase #6 $205.70   7.331%   $220.7799   $220.78   $220.80   $220.80  
  Purchase #7 $141.92   12.118%   $159.1179   $159.12   $159.10   $159.10  
  7 purchase totals = $1,101.61       $1,187.8493   $1,187.86   $1,187.90   $1,187.90