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 $224.44   7.384%   $241.0126   $241.01   $241.00   $241.00  
  Purchase #2 $120.83   4.245%   $125.9592   $125.96   $125.95   $126.00  
  Purchase #3 $184.57   10.269%   $203.5235   $203.52   $203.50   $203.50  
  Purchase #4 $243.30   5.407%   $256.4552   $256.46   $256.45   $256.50  
  Purchase #5 $131.61   7.790%   $141.8624   $141.86   $141.85   $141.90  
  Purchase #6 $58.32   8.712%   $63.4008   $63.40   $63.40   $63.40  
  Purchase #7 $5.47   13.214%   $6.1928   $6.19   $6.20   $6.20  
  7 purchase totals = $968.54       $1,038.4065   $1,038.40   $1,038.35   $1,038.50