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 $205.98   3.295%   $212.767   $212.77   $212.75   $212.80  
  Purchase #2 $17.97   4.507%   $18.7799   $18.78   $18.80   $18.80  
  Purchase #3 $99.29   4.466%   $103.7243   $103.72   $103.70   $103.70  
  Purchase #4 $15.29   8.475%   $16.5858   $16.59   $16.60   $16.60  
  Purchase #5 $221.25   7.714%   $238.3172   $238.32   $238.30   $238.30  
  Purchase #6 $155.57   3.723%   $161.3619   $161.36   $161.35   $161.40  
  Purchase #7 $191.65   5.483%   $202.1582   $202.16   $202.15   $202.20  
  7 purchase totals = $907.00       $953.6943   $953.70   $953.65   $953.80