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 $212.74   13.352%   $241.145   $241.15   $241.15   $241.10  
  Purchase #2 $244.50   5.263%   $257.368   $257.37   $257.35   $257.40  
  Purchase #3 $242.62   6.690%   $258.8513   $258.85   $258.85   $258.90  
  Purchase #4 $218.28   5.556%   $230.4076   $230.41   $230.40   $230.40  
  Purchase #5 $132.76   13.225%   $150.3175   $150.32   $150.30   $150.30  
  Purchase #6 $230.92   4.722%   $241.824   $241.82   $241.80   $241.80  
  Purchase #7 $130.49   3.433%   $134.9697   $134.97   $134.95   $135.00  
  7 purchase totals = $1,412.31       $1,514.8831   $1,514.89   $1,514.80   $1,514.90