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 $59.34   9.766%   $65.1351   $65.14   $65.15   $65.10  
  Purchase #2 $227.30   8.136%   $245.7931   $245.79   $245.80   $245.80  
  Purchase #3 $155.99   11.461%   $173.868   $173.87   $173.85   $173.90  
  Purchase #4 $46.65   8.734%   $50.7244   $50.72   $50.70   $50.70  
  Purchase #5 $229.95   5.139%   $241.7671   $241.77   $241.75   $241.80  
  Purchase #6 $39.41   6.229%   $41.8648   $41.86   $41.85   $41.90  
  Purchase #7 $27.33   7.637%   $29.4172   $29.42   $29.40   $29.40  
  7 purchase totals = $785.97       $848.5697   $848.57   $848.50   $848.60