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 $249.79   5.750%   $264.1529   $264.15   $264.15   $264.20  
  Purchase #2 $57.71   9.206%   $63.0228   $63.02   $63.00   $63.00  
  Purchase #3 $219.65   4.722%   $230.0219   $230.02   $230.00   $230.00  
  Purchase #4 $88.35   7.361%   $94.8534   $94.85   $94.85   $94.90  
  Purchase #5 $202.85   11.131%   $225.4292   $225.43   $225.45   $225.40  
  Purchase #6 $63.83   9.609%   $69.9634   $69.96   $69.95   $70.00  
  Purchase #7 $199.59   9.295%   $218.1419   $218.14   $218.15   $218.10  
  7 purchase totals = $1,081.77       $1,165.5855   $1,165.57   $1,165.55   $1,165.60