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 $182.59   13.767%   $207.7272   $207.73   $207.75   $207.70  
  Purchase #2 $135.75   13.261%   $153.7518   $153.75   $153.75   $153.80  
  Purchase #3 $230.45   4.704%   $241.2904   $241.29   $241.30   $241.30  
  Purchase #4 $141.88   12.411%   $159.4887   $159.49   $159.50   $159.50  
  Purchase #5 $169.55   3.443%   $175.3876   $175.39   $175.40   $175.40  
  Purchase #6 $212.39   6.852%   $226.943   $226.94   $226.95   $226.90  
  Purchase #7 $231.52   6.122%   $245.6937   $245.69   $245.70   $245.70  
  7 purchase totals = $1,304.13       $1,410.2824   $1,410.28   $1,410.35   $1,410.30