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 $208.48   11.449%   $232.3489   $232.35   $232.35   $232.30  
  Purchase #2 $11.94   11.427%   $13.3044   $13.30   $13.30   $13.30  
  Purchase #3 $230.31   9.684%   $252.6132   $252.61   $252.60   $252.60  
  Purchase #4 $204.38   7.363%   $219.4285   $219.43   $219.45   $219.40  
  Purchase #5 $60.34   4.691%   $63.1705   $63.17   $63.15   $63.20  
  Purchase #6 $203.46   8.774%   $221.3116   $221.31   $221.30   $221.30  
  Purchase #7 $85.37   12.681%   $96.1958   $96.20   $96.20   $96.20  
  7 purchase totals = $1,004.28       $1,098.3729   $1,098.37   $1,098.35   $1,098.30