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 $62.49   10.147%   $68.8309   $68.83   $68.85   $68.80  
  Purchase #2 $201.72   9.370%   $220.6212   $220.62   $220.60   $220.60  
  Purchase #3 $57.76   8.247%   $62.5235   $62.52   $62.50   $62.50  
  Purchase #4 $228.50   8.303%   $247.4724   $247.47   $247.45   $247.50  
  Purchase #5 $124.31   6.592%   $132.5045   $132.50   $132.50   $132.50  
  Purchase #6 $112.81   6.354%   $119.9779   $119.98   $120.00   $120.00  
  Purchase #7 $130.43   9.482%   $142.7974   $142.80   $142.80   $142.80  
  7 purchase totals = $918.02       $994.7278   $994.72   $994.70   $994.70