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 $193.57   4.852%   $202.962   $202.96   $202.95   $203.00  
  Purchase #2 $116.87   12.449%   $131.4191   $131.42   $131.40   $131.40  
  Purchase #3 $66.26   12.671%   $74.6558   $74.66   $74.65   $74.70  
  Purchase #4 $209.78   3.696%   $217.5335   $217.53   $217.55   $217.50  
  Purchase #5 $11.72   13.265%   $13.2747   $13.27   $13.25   $13.30  
  Purchase #6 $30.50   13.793%   $34.7069   $34.71   $34.70   $34.70  
  Purchase #7 $56.59   12.400%   $63.6072   $63.61   $63.60   $63.60  
  7 purchase totals = $685.29       $738.1592   $738.16   $738.10   $738.20