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 $228.46   7.736%   $246.1337   $246.13   $246.15   $246.10  
  Purchase #2 $94.66   10.279%   $104.3901   $104.39   $104.40   $104.40  
  Purchase #3 $11.71   7.830%   $12.6269   $12.63   $12.65   $12.60  
  Purchase #4 $93.66   5.306%   $98.6296   $98.63   $98.65   $98.60  
  Purchase #5 $208.37   7.765%   $224.5499   $224.55   $224.55   $224.50  
  Purchase #6 $97.70   10.270%   $107.7338   $107.73   $107.75   $107.70  
  Purchase #7 $38.37   7.416%   $41.2155   $41.22   $41.20   $41.20  
  7 purchase totals = $772.93       $835.2795   $835.28   $835.35   $835.10