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 $194.45   7.839%   $209.6929   $209.69   $209.70   $209.70  
  Purchase #2 $24.73   8.177%   $26.7522   $26.75   $26.75   $26.80  
  Purchase #3 $241.69   5.455%   $254.8742   $254.87   $254.85   $254.90  
  Purchase #4 $92.86   7.213%   $99.558   $99.56   $99.55   $99.60  
  Purchase #5 $26.88   12.556%   $30.2551   $30.26   $30.25   $30.30  
  Purchase #6 $172.85   9.275%   $188.8818   $188.88   $188.90   $188.90  
  Purchase #7 $211.28   4.367%   $220.5066   $220.51   $220.50   $220.50  
  7 purchase totals = $964.74       $1,030.5208   $1,030.52   $1,030.50   $1,030.70