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 $188.31   3.195%   $194.3265   $194.33   $194.35   $194.30  
  Purchase #2 $219.39   6.496%   $233.6416   $233.64   $233.65   $233.60  
  Purchase #3 $238.90   5.689%   $252.491   $252.49   $252.50   $252.50  
  Purchase #4 $125.59   6.393%   $133.619   $133.62   $133.60   $133.60  
  Purchase #5 $28.85   11.508%   $32.1701   $32.17   $32.15   $32.20  
  Purchase #6 $6.82   12.448%   $7.669   $7.67   $7.65   $7.70  
  Purchase #7 $169.34   6.725%   $180.7281   $180.73   $180.75   $180.70  
  7 purchase totals = $977.20       $1,034.6453   $1,034.65   $1,034.65   $1,034.60