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 $104.98   5.814%   $111.0835   $111.08   $111.10   $111.10  
  Purchase #2 $17.44   9.351%   $19.0708   $19.07   $19.05   $19.10  
  Purchase #3 $66.34   10.490%   $73.2991   $73.30   $73.30   $73.30  
  Purchase #4 $245.77   7.268%   $263.6326   $263.63   $263.65   $263.60  
  Purchase #5 $130.41   11.149%   $144.9494   $144.95   $144.95   $144.90  
  Purchase #6 $159.71   7.427%   $171.5717   $171.57   $171.55   $171.60  
  Purchase #7 $39.56   5.304%   $41.6583   $41.66   $41.65   $41.70  
  7 purchase totals = $764.21       $825.2654   $825.26   $825.25   $825.30