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 $62.76   10.532%   $69.3699   $69.37   $69.35   $69.40  
  Purchase #2 $31.29   3.797%   $32.4781   $32.48   $32.50   $32.50  
  Purchase #3 $104.28   13.135%   $117.9772   $117.98   $118.00   $118.00  
  Purchase #4 $250.67   3.707%   $259.9623   $259.96   $259.95   $260.00  
  Purchase #5 $49.52   11.540%   $55.2346   $55.23   $55.25   $55.20  
  Purchase #6 $32.84   3.382%   $33.9506   $33.95   $33.95   $34.00  
  Purchase #7 $176.78   13.720%   $201.0342   $201.03   $201.05   $201.00  
  7 purchase totals = $708.14       $770.0069   $770.00   $770.05   $770.10