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 $201.26   13.214%   $227.8545   $227.85   $227.85   $227.90  
  Purchase #2 $117.86   7.569%   $126.7808   $126.78   $126.80   $126.80  
  Purchase #3 $61.69   5.515%   $65.0922   $65.09   $65.10   $65.10  
  Purchase #4 $225.99   13.751%   $257.0659   $257.07   $257.05   $257.10  
  Purchase #5 $102.30   5.226%   $107.6462   $107.65   $107.65   $107.60  
  Purchase #6 $101.26   4.346%   $105.6608   $105.66   $105.65   $105.70  
  Purchase #7 $179.44   8.398%   $194.5094   $194.51   $194.50   $194.50  
  7 purchase totals = $989.80       $1,084.6098   $1,084.61   $1,084.60   $1,084.70