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 $65.90   3.161%   $67.9831   $67.98   $68.00   $68.00  
  Purchase #2 $79.43   10.560%   $87.8178   $87.82   $87.80   $87.80  
  Purchase #3 $216.85   10.583%   $239.7992   $239.80   $239.80   $239.80  
  Purchase #4 $246.63   10.675%   $272.9578   $272.96   $272.95   $273.00  
  Purchase #5 $150.88   5.624%   $159.3655   $159.37   $159.35   $159.40  
  Purchase #6 $158.42   10.663%   $175.3123   $175.31   $175.30   $175.30  
  Purchase #7 $230.62   4.511%   $241.0233   $241.02   $241.00   $241.00  
  7 purchase totals = $1,148.73       $1,244.2590   $1,244.26   $1,244.20   $1,244.30