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 $91.89   6.373%   $97.7461   $97.75   $97.75   $97.70  
  Purchase #2 $244.96   4.318%   $255.5374   $255.54   $255.55   $255.50  
  Purchase #3 $42.44   4.284%   $44.2581   $44.26   $44.25   $44.30  
  Purchase #4 $203.66   11.790%   $227.6715   $227.67   $227.65   $227.70  
  Purchase #5 $225.65   7.642%   $242.8942   $242.89   $242.90   $242.90  
  Purchase #6 $51.27   9.248%   $56.0114   $56.01   $56.00   $56.00  
  Purchase #7 $85.72   12.578%   $96.5019   $96.50   $96.50   $96.50  
  7 purchase totals = $945.59       $1,020.6206   $1,020.62   $1,020.60   $1,020.60