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 $200.85   11.761%   $224.472   $224.47   $224.45   $224.50  
  Purchase #2 $135.83   13.266%   $153.8492   $153.85   $153.85   $153.80  
  Purchase #3 $108.67   10.446%   $120.0217   $120.02   $120.00   $120.00  
  Purchase #4 $248.45   7.224%   $266.398   $266.40   $266.40   $266.40  
  Purchase #5 $224.84   3.526%   $232.7679   $232.77   $232.75   $232.80  
  Purchase #6 $99.93   7.587%   $107.5117   $107.51   $107.50   $107.50  
  Purchase #7 $10.45   5.216%   $10.9951   $11.00   $11.00   $11.00  
  7 purchase totals = $1,029.02       $1,116.0156   $1,116.02   $1,115.95   $1,116.00