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 $162.97   10.605%   $180.253   $180.25   $180.25   $180.30  
  Purchase #2 $64.64   10.791%   $71.6153   $71.62   $71.60   $71.60  
  Purchase #3 $90.66   6.834%   $96.8557   $96.86   $96.85   $96.90  
  Purchase #4 $143.95   7.155%   $154.2496   $154.25   $154.25   $154.20  
  Purchase #5 $239.97   12.400%   $269.7263   $269.73   $269.75   $269.70  
  Purchase #6 $58.97   12.416%   $66.2917   $66.29   $66.30   $66.30  
  Purchase #7 $147.60   10.405%   $162.9578   $162.96   $162.95   $163.00  
  7 purchase totals = $908.76       $1,001.9494   $1,001.96   $1,001.95   $1,002.00