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 $209.87   12.573%   $236.257   $236.26   $236.25   $236.30  
  Purchase #2 $81.85   7.593%   $88.0649   $88.06   $88.05   $88.10  
  Purchase #3 $189.30   4.541%   $197.8961   $197.90   $197.90   $197.90  
  Purchase #4 $247.36   11.696%   $276.2912   $276.29   $276.30   $276.30  
  Purchase #5 $206.96   12.559%   $232.9521   $232.95   $232.95   $233.00  
  Purchase #6 $232.46   5.649%   $245.5917   $245.59   $245.60   $245.60  
  Purchase #7 $212.37   3.260%   $219.2933   $219.29   $219.30   $219.30  
  7 purchase totals = $1,380.17       $1,496.3463   $1,496.34   $1,496.35   $1,496.50