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 $54.70   13.302%   $61.9762   $61.98   $62.00   $62.00  
  Purchase #2 $140.98   4.389%   $147.1676   $147.17   $147.15   $147.20  
  Purchase #3 $232.62   5.238%   $244.8046   $244.80   $244.80   $244.80  
  Purchase #4 $142.62   12.235%   $160.0696   $160.07   $160.05   $160.10  
  Purchase #5 $30.94   10.260%   $34.1144   $34.11   $34.10   $34.10  
  Purchase #6 $208.89   11.579%   $233.0774   $233.08   $233.10   $233.10  
  Purchase #7 $92.34   9.201%   $100.8362   $100.84   $100.85   $100.80  
  7 purchase totals = $903.09       $982.0460   $982.05   $982.05   $982.10