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 $247.47   5.164%   $260.2494   $260.25   $260.25   $260.20  
  Purchase #2 $91.42   3.872%   $94.9598   $94.96   $94.95   $95.00  
  Purchase #3 $89.67   5.604%   $94.6951   $94.70   $94.70   $94.70  
  Purchase #4 $151.26   12.427%   $170.0571   $170.06   $170.05   $170.10  
  Purchase #5 $37.92   3.413%   $39.2142   $39.21   $39.20   $39.20  
  Purchase #6 $98.93   12.260%   $111.0588   $111.06   $111.05   $111.10  
  Purchase #7 $85.33   8.572%   $92.6445   $92.64   $92.65   $92.60  
  7 purchase totals = $802.00       $862.8789   $862.88   $862.85   $862.90