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 $55.90   6.802%   $59.7023   $59.70   $59.70   $59.70  
  Purchase #2 $216.82   9.120%   $236.594   $236.59   $236.60   $236.60  
  Purchase #3 $55.43   6.467%   $59.0147   $59.01   $59.00   $59.00  
  Purchase #4 $203.34   13.388%   $230.5632   $230.56   $230.55   $230.60  
  Purchase #5 $121.44   3.582%   $125.79   $125.79   $125.80   $125.80  
  Purchase #6 $153.99   7.804%   $166.0074   $166.01   $166.00   $166.00  
  Purchase #7 $7.63   9.210%   $8.3327   $8.33   $8.35   $8.30  
  7 purchase totals = $814.55       $886.0043   $885.99   $886.00   $886.00