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 $192.52   6.115%   $204.2926   $204.29   $204.30   $204.30  
  Purchase #2 $67.96   8.146%   $73.496   $73.50   $73.50   $73.50  
  Purchase #3 $76.81   10.678%   $85.0118   $85.01   $85.00   $85.00  
  Purchase #4 $140.77   10.136%   $155.0384   $155.04   $155.05   $155.00  
  Purchase #5 $157.73   8.540%   $171.2001   $171.20   $171.20   $171.20  
  Purchase #6 $56.69   10.270%   $62.5121   $62.51   $62.50   $62.50  
  Purchase #7 $93.89   3.626%   $97.2945   $97.29   $97.30   $97.30  
  7 purchase totals = $786.37       $848.8455   $848.84   $848.85   $848.80