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 $22.31   9.563%   $24.4435   $24.44   $24.45   $24.40  
  Purchase #2 $208.61   12.840%   $235.3955   $235.40   $235.40   $235.40  
  Purchase #3 $59.26   9.854%   $65.0995   $65.10   $65.10   $65.10  
  Purchase #4 $167.53   5.873%   $177.369   $177.37   $177.35   $177.40  
  Purchase #5 $250.65   9.690%   $274.938   $274.94   $274.95   $274.90  
  Purchase #6 $206.98   5.811%   $219.0076   $219.01   $219.00   $219.00  
  Purchase #7 $64.41   12.360%   $72.3711   $72.37   $72.35   $72.40  
  7 purchase totals = $979.75       $1,068.6242   $1,068.63   $1,068.60   $1,068.60