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 $234.83   4.604%   $245.6416   $245.64   $245.65   $245.60  
  Purchase #2 $197.53   7.657%   $212.6549   $212.65   $212.65   $212.70  
  Purchase #3 $219.25   7.525%   $235.7486   $235.75   $235.75   $235.70  
  Purchase #4 $129.66   5.536%   $136.838   $136.84   $136.85   $136.80  
  Purchase #5 $24.60   6.429%   $26.1815   $26.18   $26.20   $26.20  
  Purchase #6 $163.82   13.750%   $186.3453   $186.35   $186.35   $186.30  
  Purchase #7 $234.73   10.284%   $258.8696   $258.87   $258.85   $258.90  
  7 purchase totals = $1,204.42       $1,302.2795   $1,302.28   $1,302.30   $1,302.20