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 $155.40   9.727%   $170.5158   $170.52   $170.50   $170.50  
  Purchase #2 $23.80   4.310%   $24.8258   $24.83   $24.85   $24.80  
  Purchase #3 $232.38   7.745%   $250.3778   $250.38   $250.40   $250.40  
  Purchase #4 $132.62   4.789%   $138.9712   $138.97   $138.95   $139.00  
  Purchase #5 $42.81   9.207%   $46.7515   $46.75   $46.75   $46.80  
  Purchase #6 $44.71   12.329%   $50.2223   $50.22   $50.20   $50.20  
  Purchase #7 $95.37   8.190%   $103.1808   $103.18   $103.20   $103.20  
  7 purchase totals = $727.09       $784.8452   $784.85   $784.85   $784.90