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 $56.81   13.458%   $64.4555   $64.46   $64.45   $64.50  
  Purchase #2 $210.73   9.434%   $230.6103   $230.61   $230.60   $230.60  
  Purchase #3 $100.61   6.235%   $106.883   $106.88   $106.90   $106.90  
  Purchase #4 $49.49   5.280%   $52.1031   $52.10   $52.10   $52.10  
  Purchase #5 $199.59   10.214%   $219.9761   $219.98   $220.00   $220.00  
  Purchase #6 $211.76   3.391%   $218.9408   $218.94   $218.95   $218.90  
  Purchase #7 $125.76   11.510%   $140.235   $140.24   $140.25   $140.20  
  7 purchase totals = $954.75       $1,033.2038   $1,033.21   $1,033.25   $1,033.20