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 $134.74   13.147%   $152.4543   $152.45   $152.45   $152.50  
  Purchase #2 $238.96   3.512%   $247.3523   $247.35   $247.35   $247.40  
  Purchase #3 $79.73   11.394%   $88.8144   $88.81   $88.80   $88.80  
  Purchase #4 $8.38   12.371%   $9.4167   $9.42   $9.40   $9.40  
  Purchase #5 $171.73   6.155%   $182.3   $182.30   $182.30   $182.30  
  Purchase #6 $200.47   12.344%   $225.216   $225.22   $225.20   $225.20  
  Purchase #7 $127.76   13.343%   $144.807   $144.81   $144.80   $144.80  
  7 purchase totals = $961.77       $1,050.3607   $1,050.36   $1,050.30   $1,050.40