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 $241.49   13.288%   $273.5792   $273.58   $273.60   $273.60  
  Purchase #2 $151.64   9.189%   $165.5742   $165.57   $165.55   $165.60  
  Purchase #3 $229.88   7.144%   $246.3026   $246.30   $246.30   $246.30  
  Purchase #4 $198.97   5.122%   $209.1612   $209.16   $209.15   $209.20  
  Purchase #5 $197.75   4.134%   $205.925   $205.93   $205.95   $205.90  
  Purchase #6 $29.43   6.750%   $31.4165   $31.42   $31.40   $31.40  
  Purchase #7 $66.84   6.157%   $70.9553   $70.96   $70.95   $71.00  
  7 purchase totals = $1,116.00       $1,202.9140   $1,202.92   $1,202.90   $1,203.00