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 $196.58   12.251%   $220.663   $220.66   $220.65   $220.70  
  Purchase #2 $61.84   6.639%   $65.9456   $65.95   $65.95   $65.90  
  Purchase #3 $82.86   6.824%   $88.5144   $88.51   $88.50   $88.50  
  Purchase #4 $97.36   9.578%   $106.6851   $106.69   $106.70   $106.70  
  Purchase #5 $95.81   6.294%   $101.8403   $101.84   $101.85   $101.80  
  Purchase #6 $72.62   3.872%   $75.4318   $75.43   $75.45   $75.40  
  Purchase #7 $42.40   5.545%   $44.7511   $44.75   $44.75   $44.80  
  7 purchase totals = $649.47       $703.8313   $703.83   $703.85   $703.80