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 $246.56   11.729%   $275.479   $275.48   $275.50   $275.50  
  Purchase #2 $84.53   12.333%   $94.9551   $94.96   $94.95   $95.00  
  Purchase #3 $236.58   11.451%   $263.6708   $263.67   $263.65   $263.70  
  Purchase #4 $173.55   13.638%   $197.2187   $197.22   $197.20   $197.20  
  Purchase #5 $159.45   9.828%   $175.1207   $175.12   $175.10   $175.10  
  Purchase #6 $91.67   9.551%   $100.4254   $100.43   $100.45   $100.40  
  Purchase #7 $213.48   12.236%   $239.6014   $239.60   $239.60   $239.60  
  7 purchase totals = $1,205.82       $1,346.4711   $1,346.48   $1,346.45   $1,346.50