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 $199.41   3.453%   $206.2956   $206.30   $206.30   $206.30  
  Purchase #2 $45.62   9.413%   $49.9142   $49.91   $49.90   $49.90  
  Purchase #3 $169.95   7.481%   $182.664   $182.66   $182.65   $182.70  
  Purchase #4 $156.45   11.302%   $174.132   $174.13   $174.15   $174.10  
  Purchase #5 $182.54   11.770%   $204.025   $204.03   $204.05   $204.00  
  Purchase #6 $68.28   13.463%   $77.4725   $77.47   $77.45   $77.50  
  Purchase #7 $99.51   12.850%   $112.297   $112.30   $112.30   $112.30  
  7 purchase totals = $921.76       $1,006.8003   $1,006.80   $1,006.80   $1,006.80