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 $59.78   3.705%   $61.9948   $61.99   $62.00   $62.00  
  Purchase #2 $183.25   6.869%   $195.8374   $195.84   $195.85   $195.80  
  Purchase #3 $183.37   4.553%   $191.7188   $191.72   $191.70   $191.70  
  Purchase #4 $90.92   11.658%   $101.5195   $101.52   $101.50   $101.50  
  Purchase #5 $39.61   3.217%   $40.8843   $40.88   $40.90   $40.90  
  Purchase #6 $221.73   11.351%   $246.8986   $246.90   $246.90   $246.90  
  Purchase #7 $22.91   10.644%   $25.3485   $25.35   $25.35   $25.30  
  7 purchase totals = $801.57       $864.2019   $864.20   $864.20   $864.10