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 $64.55   4.227%   $67.2785   $67.28   $67.30   $67.30  
  Purchase #2 $195.52   11.137%   $217.2951   $217.30   $217.30   $217.30  
  Purchase #3 $218.32   5.682%   $230.7249   $230.72   $230.70   $230.70  
  Purchase #4 $231.87   4.325%   $241.8984   $241.90   $241.90   $241.90  
  Purchase #5 $79.88   10.310%   $88.1156   $88.12   $88.10   $88.10  
  Purchase #6 $123.87   11.354%   $137.9342   $137.93   $137.95   $137.90  
  Purchase #7 $45.83   12.506%   $51.5615   $51.56   $51.55   $51.60  
  7 purchase totals = $959.84       $1,034.8082   $1,034.81   $1,034.80   $1,034.80