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 $95.92   6.637%   $102.2862   $102.29   $102.30   $102.30  
  Purchase #2 $215.88   4.711%   $226.0501   $226.05   $226.05   $226.10  
  Purchase #3 $243.74   7.820%   $262.8005   $262.80   $262.80   $262.80  
  Purchase #4 $64.89   8.489%   $70.3985   $70.40   $70.40   $70.40  
  Purchase #5 $70.27   6.710%   $74.9851   $74.99   $75.00   $75.00  
  Purchase #6 $162.94   3.667%   $168.915   $168.92   $168.90   $168.90  
  Purchase #7 $222.57   9.111%   $242.8484   $242.85   $242.85   $242.80  
  7 purchase totals = $1,076.21       $1,148.2838   $1,148.30   $1,148.30   $1,148.30