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 $148.59   11.819%   $166.1519   $166.15   $166.15   $166.20  
  Purchase #2 $117.48   4.457%   $122.7161   $122.72   $122.70   $122.70  
  Purchase #3 $48.89   8.761%   $53.1733   $53.17   $53.15   $53.20  
  Purchase #4 $52.82   5.823%   $55.8957   $55.90   $55.90   $55.90  
  Purchase #5 $147.60   9.432%   $161.5216   $161.52   $161.50   $161.50  
  Purchase #6 $58.80   7.115%   $62.9836   $62.98   $63.00   $63.00  
  Purchase #7 $130.48   8.748%   $141.8944   $141.89   $141.90   $141.90  
  7 purchase totals = $704.66       $764.3366   $764.33   $764.30   $764.40