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 $246.71   6.817%   $263.5282   $263.53   $263.55   $263.50  
  Purchase #2 $201.65   4.645%   $211.0166   $211.02   $211.00   $211.00  
  Purchase #3 $11.39   8.606%   $12.3702   $12.37   $12.35   $12.40  
  Purchase #4 $178.38   5.364%   $187.9483   $187.95   $187.95   $187.90  
  Purchase #5 $214.93   3.448%   $222.3408   $222.34   $222.35   $222.30  
  Purchase #6 $203.86   11.311%   $226.9186   $226.92   $226.90   $226.90  
  Purchase #7 $205.97   9.818%   $226.1921   $226.19   $226.20   $226.20  
  7 purchase totals = $1,262.89       $1,350.3148   $1,350.32   $1,350.30   $1,350.20