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 $206.52   13.797%   $235.0136   $235.01   $235.00   $235.00  
  Purchase #2 $51.53   10.282%   $56.8283   $56.83   $56.85   $56.80  
  Purchase #3 $154.94   9.419%   $169.5338   $169.53   $169.55   $169.50  
  Purchase #4 $123.33   7.849%   $133.0102   $133.01   $133.00   $133.00  
  Purchase #5 $44.52   3.248%   $45.966   $45.97   $45.95   $46.00  
  Purchase #6 $29.41   6.136%   $31.2146   $31.21   $31.20   $31.20  
  Purchase #7 $97.36   4.445%   $101.6877   $101.69   $101.70   $101.70  
  7 purchase totals = $707.61       $773.2542   $773.25   $773.25   $773.20