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 $214.98   11.406%   $239.5006   $239.50   $239.50   $239.50  
  Purchase #2 $34.87   5.725%   $36.8663   $36.87   $36.85   $36.90  
  Purchase #3 $211.46   3.785%   $219.4638   $219.46   $219.45   $219.50  
  Purchase #4 $121.36   9.791%   $133.2424   $133.24   $133.25   $133.20  
  Purchase #5 $93.63   11.444%   $104.345   $104.35   $104.35   $104.30  
  Purchase #6 $25.41   10.474%   $28.0714   $28.07   $28.05   $28.10  
  Purchase #7 $236.87   13.578%   $269.0322   $269.03   $269.05   $269.00  
  7 purchase totals = $938.58       $1,030.5217   $1,030.52   $1,030.50   $1,030.50