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 $51.33   4.424%   $53.6008   $53.60   $53.60   $53.60  
  Purchase #2 $15.33   8.819%   $16.682   $16.68   $16.70   $16.70  
  Purchase #3 $238.58   11.754%   $266.6227   $266.62   $266.60   $266.60  
  Purchase #4 $241.64   6.276%   $256.8053   $256.81   $256.80   $256.80  
  Purchase #5 $92.78   3.515%   $96.0412   $96.04   $96.05   $96.00  
  Purchase #6 $6.40   5.624%   $6.7599   $6.76   $6.75   $6.80  
  Purchase #7 $238.45   13.237%   $270.0136   $270.01   $270.00   $270.00  
  7 purchase totals = $884.51       $966.5255   $966.52   $966.50   $966.50