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 $58.86   4.447%   $61.4775   $61.48   $61.50   $61.50  
  Purchase #2 $224.26   12.213%   $251.6489   $251.65   $251.65   $251.60  
  Purchase #3 $130.40   13.347%   $147.8045   $147.80   $147.80   $147.80  
  Purchase #4 $222.50   5.311%   $234.317   $234.32   $234.30   $234.30  
  Purchase #5 $216.82   7.463%   $233.0013   $233.00   $233.00   $233.00  
  Purchase #6 $87.36   11.784%   $97.6545   $97.65   $97.65   $97.70  
  Purchase #7 $201.51   9.728%   $221.1129   $221.11   $221.10   $221.10  
  7 purchase totals = $1,141.71       $1,247.0166   $1,247.01   $1,247.00   $1,247.00