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 $173.61   12.220%   $194.8251   $194.83   $194.85   $194.80  
  Purchase #2 $51.55   12.438%   $57.9618   $57.96   $57.95   $58.00  
  Purchase #3 $53.27   3.653%   $55.216   $55.22   $55.20   $55.20  
  Purchase #4 $247.50   7.773%   $266.7382   $266.74   $266.75   $266.70  
  Purchase #5 $35.87   6.824%   $38.3178   $38.32   $38.30   $38.30  
  Purchase #6 $174.25   3.819%   $180.9046   $180.90   $180.90   $180.90  
  Purchase #7 $250.83   11.124%   $278.7323   $278.73   $278.75   $278.70  
  7 purchase totals = $986.88       $1,072.6958   $1,072.70   $1,072.70   $1,072.60