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 $181.33   10.835%   $200.9771   $200.98   $201.00   $201.00  
  Purchase #2 $99.98   4.870%   $104.849   $104.85   $104.85   $104.80  
  Purchase #3 $21.29   4.734%   $22.2979   $22.30   $22.30   $22.30  
  Purchase #4 $243.77   12.200%   $273.5099   $273.51   $273.50   $273.50  
  Purchase #5 $80.95   10.178%   $89.1891   $89.19   $89.20   $89.20  
  Purchase #6 $98.89   5.807%   $104.6325   $104.63   $104.65   $104.60  
  Purchase #7 $125.26   8.386%   $135.7643   $135.76   $135.75   $135.80  
  7 purchase totals = $851.47       $931.2198   $931.22   $931.25   $931.20