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 $151.96   7.239%   $162.9604   $162.96   $162.95   $163.00  
  Purchase #2 $97.41   9.644%   $106.8042   $106.80   $106.80   $106.80  
  Purchase #3 $10.85   9.400%   $11.8699   $11.87   $11.85   $11.90  
  Purchase #4 $119.46   4.371%   $124.6816   $124.68   $124.70   $124.70  
  Purchase #5 $132.81   10.222%   $146.3858   $146.39   $146.40   $146.40  
  Purchase #6 $64.72   11.264%   $72.0101   $72.01   $72.00   $72.00  
  Purchase #7 $172.80   11.776%   $193.1489   $193.15   $193.15   $193.10  
  7 purchase totals = $750.01       $817.8609   $817.86   $817.85   $817.90