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 $248.53   11.436%   $276.9519   $276.95   $276.95   $277.00  
  Purchase #2 $27.30   4.190%   $28.4439   $28.44   $28.45   $28.40  
  Purchase #3 $118.93   9.158%   $129.8216   $129.82   $129.80   $129.80  
  Purchase #4 $216.88   6.431%   $230.8276   $230.83   $230.85   $230.80  
  Purchase #5 $13.96   7.615%   $15.0231   $15.02   $15.00   $15.00  
  Purchase #6 $57.96   13.836%   $65.9793   $65.98   $66.00   $66.00  
  Purchase #7 $91.67   8.704%   $99.649   $99.65   $99.65   $99.60  
  7 purchase totals = $775.23       $846.6964   $846.69   $846.70   $846.60