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 $147.98   9.660%   $162.2749   $162.27   $162.25   $162.30  
  Purchase #2 $161.88   9.122%   $176.6467   $176.65   $176.65   $176.60  
  Purchase #3 $6.34   8.276%   $6.8647   $6.86   $6.85   $6.90  
  Purchase #4 $183.80   8.436%   $199.3054   $199.31   $199.30   $199.30  
  Purchase #5 $64.81   6.596%   $69.0849   $69.08   $69.10   $69.10  
  Purchase #6 $80.36   9.371%   $87.8905   $87.89   $87.90   $87.90  
  Purchase #7 $116.94   5.703%   $123.6091   $123.61   $123.60   $123.60  
  7 purchase totals = $762.11       $825.6762   $825.67   $825.65   $825.70