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 $249.86   7.852%   $269.479   $269.48   $269.50   $269.50  
  Purchase #2 $110.80   11.332%   $123.3559   $123.36   $123.35   $123.40  
  Purchase #3 $135.62   6.654%   $144.6442   $144.64   $144.65   $144.60  
  Purchase #4 $182.44   11.190%   $202.855   $202.86   $202.85   $202.90  
  Purchase #5 $224.42   8.562%   $243.6348   $243.63   $243.65   $243.60  
  Purchase #6 $141.55   12.428%   $159.1418   $159.14   $159.15   $159.10  
  Purchase #7 $66.96   4.393%   $69.9016   $69.90   $69.90   $69.90  
  7 purchase totals = $1,111.65       $1,213.0123   $1,213.01   $1,213.05   $1,213.00