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 $34.42   6.284%   $36.583   $36.58   $36.60   $36.60  
  Purchase #2 $52.93   8.203%   $57.2718   $57.27   $57.25   $57.30  
  Purchase #3 $211.42   3.117%   $218.01   $218.01   $218.00   $218.00  
  Purchase #4 $37.94   9.353%   $41.4885   $41.49   $41.50   $41.50  
  Purchase #5 $232.54   10.831%   $257.7264   $257.73   $257.75   $257.70  
  Purchase #6 $82.55   8.560%   $89.6163   $89.62   $89.60   $89.60  
  Purchase #7 $43.79   3.519%   $45.331   $45.33   $45.35   $45.30  
  7 purchase totals = $695.59       $746.0270   $746.03   $746.05   $746.00