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 $76.29   7.858%   $82.2849   $82.28   $82.30   $82.30  
  Purchase #2 $52.75   11.814%   $58.9819   $58.98   $59.00   $59.00  
  Purchase #3 $191.81   7.735%   $206.6465   $206.65   $206.65   $206.60  
  Purchase #4 $180.47   3.487%   $186.763   $186.76   $186.75   $186.80  
  Purchase #5 $150.35   7.742%   $161.9901   $161.99   $162.00   $162.00  
  Purchase #6 $45.80   10.303%   $50.5188   $50.52   $50.50   $50.50  
  Purchase #7 $7.39   13.732%   $8.4048   $8.40   $8.40   $8.40  
  7 purchase totals = $704.86       $755.5900   $755.58   $755.60   $755.60