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 $30.86   8.740%   $33.5572   $33.56   $33.55   $33.60  
  Purchase #2 $11.32   4.446%   $11.8233   $11.82   $11.80   $11.80  
  Purchase #3 $134.75   8.857%   $146.6848   $146.68   $146.70   $146.70  
  Purchase #4 $218.31   7.143%   $233.9039   $233.90   $233.90   $233.90  
  Purchase #5 $48.75   8.241%   $52.7675   $52.77   $52.75   $52.80  
  Purchase #6 $202.79   3.313%   $209.5084   $209.51   $209.50   $209.50  
  Purchase #7 $67.78   9.348%   $74.1161   $74.12   $74.10   $74.10  
  7 purchase totals = $714.56       $762.3612   $762.36   $762.30   $762.40