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 $74.25   10.463%   $82.0188   $82.02   $82.00   $82.00  
  Purchase #2 $249.72   7.740%   $269.0483   $269.05   $269.05   $269.00  
  Purchase #3 $119.28   5.134%   $125.4038   $125.40   $125.40   $125.40  
  Purchase #4 $199.43   5.802%   $211.0009   $211.00   $211.00   $211.00  
  Purchase #5 $147.69   5.155%   $155.3034   $155.30   $155.30   $155.30  
  Purchase #6 $163.50   4.492%   $170.8444   $170.84   $170.85   $170.80  
  Purchase #7 $211.30   3.642%   $218.9955   $219.00   $219.00   $219.00  
  7 purchase totals = $1,165.17       $1,232.6151   $1,232.61   $1,232.60   $1,232.50