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 $59.50   9.594%   $65.2084   $65.21   $65.20   $65.20  
  Purchase #2 $53.74   7.654%   $57.8533   $57.85   $57.85   $57.90  
  Purchase #3 $223.50   8.866%   $243.3155   $243.32   $243.30   $243.30  
  Purchase #4 $18.94   8.553%   $20.5599   $20.56   $20.55   $20.60  
  Purchase #5 $178.94   6.811%   $191.1276   $191.13   $191.15   $191.10  
  Purchase #6 $186.94   8.295%   $202.4467   $202.45   $202.45   $202.40  
  Purchase #7 $38.70   7.858%   $41.741   $41.74   $41.75   $41.70  
  7 purchase totals = $760.26       $822.2524   $822.26   $822.25   $822.20