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 $191.32   10.113%   $210.6682   $210.67   $210.65   $210.70  
  Purchase #2 $96.50   7.418%   $103.6584   $103.66   $103.65   $103.70  
  Purchase #3 $112.55   4.725%   $117.868   $117.87   $117.85   $117.90  
  Purchase #4 $9.43   13.763%   $10.7279   $10.73   $10.75   $10.70  
  Purchase #5 $220.72   6.331%   $234.6938   $234.69   $234.70   $234.70  
  Purchase #6 $181.82   11.451%   $202.6402   $202.64   $202.65   $202.60  
  Purchase #7 $57.91   13.590%   $65.78   $65.78   $65.80   $65.80  
  7 purchase totals = $870.25       $946.0365   $946.04   $946.05   $946.10