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 $43.67   13.452%   $49.5445   $49.54   $49.55   $49.50  
  Purchase #2 $103.43   7.106%   $110.7797   $110.78   $110.80   $110.80  
  Purchase #3 $191.82   9.282%   $209.6247   $209.62   $209.60   $209.60  
  Purchase #4 $98.85   3.840%   $102.6458   $102.65   $102.65   $102.60  
  Purchase #5 $82.36   13.652%   $93.6038   $93.60   $93.60   $93.60  
  Purchase #6 $189.51   5.392%   $199.7284   $199.73   $199.75   $199.70  
  Purchase #7 $124.61   13.281%   $141.1595   $141.16   $141.15   $141.20  
  7 purchase totals = $834.25       $907.0864   $907.08   $907.10   $907.00