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 $54.76   11.246%   $60.9183   $60.92   $60.90   $60.90  
  Purchase #2 $204.65   12.394%   $230.0143   $230.01   $230.00   $230.00  
  Purchase #3 $205.61   6.145%   $218.2447   $218.24   $218.25   $218.20  
  Purchase #4 $6.94   13.163%   $7.8535   $7.85   $7.85   $7.90  
  Purchase #5 $169.35   6.855%   $180.9589   $180.96   $180.95   $181.00  
  Purchase #6 $190.89   5.193%   $200.8029   $200.80   $200.80   $200.80  
  Purchase #7 $88.47   10.473%   $97.7355   $97.74   $97.75   $97.70  
  7 purchase totals = $920.67       $996.5281   $996.52   $996.50   $996.50