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 $62.35   6.844%   $66.6172   $66.62   $66.60   $66.60  
  Purchase #2 $14.64   4.205%   $15.2556   $15.26   $15.25   $15.30  
  Purchase #3 $90.50   3.753%   $93.8965   $93.90   $93.90   $93.90  
  Purchase #4 $110.68   8.494%   $120.0812   $120.08   $120.10   $120.10  
  Purchase #5 $215.84   6.216%   $229.2566   $229.26   $229.25   $229.30  
  Purchase #6 $131.64   12.576%   $148.195   $148.20   $148.20   $148.20  
  Purchase #7 $70.79   3.401%   $73.1976   $73.20   $73.20   $73.20  
  7 purchase totals = $696.44       $746.4997   $746.52   $746.50   $746.60