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 $147.64   12.187%   $165.6329   $165.63   $165.65   $165.60  
  Purchase #2 $207.99   8.582%   $225.8397   $225.84   $225.85   $225.80  
  Purchase #3 $178.67   3.553%   $185.0181   $185.02   $185.00   $185.00  
  Purchase #4 $245.29   3.432%   $253.7084   $253.71   $253.70   $253.70  
  Purchase #5 $227.94   11.819%   $254.8802   $254.88   $254.90   $254.90  
  Purchase #6 $150.89   5.668%   $159.4424   $159.44   $159.45   $159.40  
  Purchase #7 $47.65   4.298%   $49.698   $49.70   $49.70   $49.70  
  7 purchase totals = $1,206.07       $1,294.2197   $1,294.22   $1,294.25   $1,294.10