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 $203.67   13.287%   $230.7316   $230.73   $230.75   $230.70  
  Purchase #2 $95.49   4.329%   $99.6238   $99.62   $99.60   $99.60  
  Purchase #3 $216.39   12.715%   $243.904   $243.90   $243.90   $243.90  
  Purchase #4 $141.33   8.722%   $153.6568   $153.66   $153.65   $153.70  
  Purchase #5 $204.62   5.642%   $216.1647   $216.16   $216.15   $216.20  
  Purchase #6 $43.58   8.307%   $47.2002   $47.20   $47.20   $47.20  
  Purchase #7 $188.36   9.220%   $205.7268   $205.73   $205.75   $205.70  
  7 purchase totals = $1,093.44       $1,197.0079   $1,197.00   $1,197.00   $1,197.00