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 $77.52   8.791%   $84.3348   $84.33   $84.35   $84.30  
  Purchase #2 $107.35   9.569%   $117.6223   $117.62   $117.60   $117.60  
  Purchase #3 $204.57   12.211%   $229.55   $229.55   $229.55   $229.60  
  Purchase #4 $175.58   12.687%   $197.8558   $197.86   $197.85   $197.90  
  Purchase #5 $190.92   9.144%   $208.3777   $208.38   $208.40   $208.40  
  Purchase #6 $115.71   9.236%   $126.397   $126.40   $126.40   $126.40  
  Purchase #7 $58.36   6.256%   $62.011   $62.01   $62.00   $62.00  
  7 purchase totals = $930.01       $1,026.1486   $1,026.15   $1,026.15   $1,026.20