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 $218.73   11.525%   $243.9386   $243.94   $243.95   $243.90  
  Purchase #2 $88.81   8.853%   $96.6723   $96.67   $96.65   $96.70  
  Purchase #3 $229.44   5.277%   $241.5475   $241.55   $241.55   $241.50  
  Purchase #4 $22.55   8.385%   $24.4408   $24.44   $24.45   $24.40  
  Purchase #5 $246.79   12.501%   $277.6412   $277.64   $277.65   $277.60  
  Purchase #6 $179.99   11.115%   $199.9959   $200.00   $200.00   $200.00  
  Purchase #7 $232.44   13.444%   $263.6892   $263.69   $263.70   $263.70  
  7 purchase totals = $1,218.75       $1,347.9255   $1,347.93   $1,347.95   $1,347.80