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 $116.88   9.499%   $127.9824   $127.98   $128.00   $128.00  
  Purchase #2 $109.77   11.842%   $122.769   $122.77   $122.75   $122.80  
  Purchase #3 $8.40   7.650%   $9.0426   $9.04   $9.05   $9.00  
  Purchase #4 $63.94   11.474%   $71.2765   $71.28   $71.30   $71.30  
  Purchase #5 $73.87   10.209%   $81.4114   $81.41   $81.40   $81.40  
  Purchase #6 $112.51   4.417%   $117.4796   $117.48   $117.50   $117.50  
  Purchase #7 $99.85   7.552%   $107.3907   $107.39   $107.40   $107.40  
  7 purchase totals = $585.22       $637.3522   $637.35   $637.40   $637.40