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 $96.29   7.294%   $103.3134   $103.31   $103.30   $103.30  
  Purchase #2 $190.98   10.725%   $211.4626   $211.46   $211.45   $211.50  
  Purchase #3 $90.84   11.448%   $101.2394   $101.24   $101.25   $101.20  
  Purchase #4 $243.98   13.182%   $276.1414   $276.14   $276.15   $276.10  
  Purchase #5 $179.67   9.685%   $197.071   $197.07   $197.05   $197.10  
  Purchase #6 $151.46   10.621%   $167.5466   $167.55   $167.55   $167.50  
  Purchase #7 $237.50   3.794%   $246.5108   $246.51   $246.50   $246.50  
  7 purchase totals = $1,190.72       $1,303.2852   $1,303.28   $1,303.25   $1,303.20