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 $76.41   11.213%   $84.9779   $84.98   $85.00   $85.00  
  Purchase #2 $245.65   3.393%   $253.9849   $253.98   $254.00   $254.00  
  Purchase #3 $191.80   8.239%   $207.6024   $207.60   $207.60   $207.60  
  Purchase #4 $51.52   3.167%   $53.1516   $53.15   $53.15   $53.20  
  Purchase #5 $82.49   9.314%   $90.1731   $90.17   $90.15   $90.20  
  Purchase #6 $58.71   6.497%   $62.5244   $62.52   $62.50   $62.50  
  Purchase #7 $203.29   3.653%   $210.7162   $210.72   $210.70   $210.70  
  7 purchase totals = $909.87       $963.1305   $963.12   $963.10   $963.20