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 $232.55   9.570%   $254.805   $254.81   $254.80   $254.80  
  Purchase #2 $83.82   10.292%   $92.4468   $92.45   $92.45   $92.40  
  Purchase #3 $88.67   9.578%   $97.1628   $97.16   $97.15   $97.20  
  Purchase #4 $85.50   11.558%   $95.3821   $95.38   $95.40   $95.40  
  Purchase #5 $24.39   6.452%   $25.9636   $25.96   $25.95   $26.00  
  Purchase #6 $25.67   11.457%   $28.611   $28.61   $28.60   $28.60  
  Purchase #7 $77.46   3.752%   $80.3663   $80.37   $80.35   $80.40  
  7 purchase totals = $618.06       $674.7376   $674.74   $674.70   $674.80