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 $241.84   4.808%   $253.4677   $253.47   $253.45   $253.50  
  Purchase #2 $135.64   8.592%   $147.2942   $147.29   $147.30   $147.30  
  Purchase #3 $98.80   12.781%   $111.4276   $111.43   $111.45   $111.40  
  Purchase #4 $233.66   12.468%   $262.7927   $262.79   $262.80   $262.80  
  Purchase #5 $131.89   11.688%   $147.3053   $147.31   $147.30   $147.30  
  Purchase #6 $19.62   12.305%   $22.0342   $22.03   $22.05   $22.00  
  Purchase #7 $233.98   11.464%   $260.8035   $260.80   $260.80   $260.80  
  7 purchase totals = $1,095.43       $1,205.1252   $1,205.12   $1,205.15   $1,205.10