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 $202.63   13.757%   $230.5058   $230.51   $230.50   $230.50  
  Purchase #2 $129.63   5.415%   $136.6495   $136.65   $136.65   $136.60  
  Purchase #3 $207.30   5.425%   $218.546   $218.55   $218.55   $218.50  
  Purchase #4 $190.94   8.677%   $207.5079   $207.51   $207.50   $207.50  
  Purchase #5 $209.35   9.366%   $228.9577   $228.96   $228.95   $229.00  
  Purchase #6 $239.35   4.734%   $250.6808   $250.68   $250.70   $250.70  
  Purchase #7 $27.93   11.455%   $31.1294   $31.13   $31.15   $31.10  
  7 purchase totals = $1,207.13       $1,303.9771   $1,303.99   $1,304.00   $1,303.90