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 $87.74   7.858%   $94.6346   $94.63   $94.65   $94.60  
  Purchase #2 $32.94   4.449%   $34.4055   $34.41   $34.40   $34.40  
  Purchase #3 $132.44   6.371%   $140.8778   $140.88   $140.90   $140.90  
  Purchase #4 $228.59   5.584%   $241.3545   $241.35   $241.35   $241.40  
  Purchase #5 $102.93   4.472%   $107.533   $107.53   $107.55   $107.50  
  Purchase #6 $228.85   5.564%   $241.5832   $241.58   $241.60   $241.60  
  Purchase #7 $60.62   7.306%   $65.0489   $65.05   $65.05   $65.00  
  7 purchase totals = $874.11       $925.4375   $925.43   $925.50   $925.40