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 $94.78   3.852%   $98.4309   $98.43   $98.45   $98.40  
  Purchase #2 $66.80   13.154%   $75.5869   $75.59   $75.60   $75.60  
  Purchase #3 $247.44   10.403%   $273.1812   $273.18   $273.20   $273.20  
  Purchase #4 $234.61   5.435%   $247.3611   $247.36   $247.35   $247.40  
  Purchase #5 $229.49   13.375%   $260.1843   $260.18   $260.20   $260.20  
  Purchase #6 $66.25   6.140%   $70.3178   $70.32   $70.30   $70.30  
  Purchase #7 $140.92   6.798%   $150.4997   $150.50   $150.50   $150.50  
  7 purchase totals = $1,080.29       $1,175.5619   $1,175.56   $1,175.60   $1,175.60