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 $59.43   4.114%   $61.875   $61.88   $61.90   $61.90  
  Purchase #2 $33.66   3.505%   $34.8398   $34.84   $34.85   $34.80  
  Purchase #3 $225.31   4.543%   $235.5458   $235.55   $235.55   $235.50  
  Purchase #4 $35.64   11.168%   $39.6203   $39.62   $39.60   $39.60  
  Purchase #5 $170.51   7.498%   $183.2948   $183.29   $183.30   $183.30  
  Purchase #6 $106.67   12.266%   $119.7541   $119.75   $119.75   $119.80  
  Purchase #7 $142.82   12.412%   $160.5468   $160.55   $160.55   $160.50  
  7 purchase totals = $774.04       $835.4766   $835.48   $835.50   $835.40