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 $75.98   8.550%   $82.4763   $82.48   $82.50   $82.50  
  Purchase #2 $118.52   5.641%   $125.2057   $125.21   $125.20   $125.20  
  Purchase #3 $45.41   13.508%   $51.544   $51.54   $51.55   $51.50  
  Purchase #4 $240.78   4.731%   $252.1713   $252.17   $252.15   $252.20  
  Purchase #5 $48.97   8.126%   $52.9493   $52.95   $52.95   $52.90  
  Purchase #6 $216.38   13.459%   $245.5026   $245.50   $245.50   $245.50  
  Purchase #7 $213.53   4.803%   $223.7858   $223.79   $223.80   $223.80  
  7 purchase totals = $959.57       $1,033.6350   $1,033.64   $1,033.65   $1,033.60