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 $49.93   5.764%   $52.808   $52.81   $52.80   $52.80  
  Purchase #2 $157.26   4.637%   $164.5521   $164.55   $164.55   $164.60  
  Purchase #3 $225.70   9.165%   $246.3854   $246.39   $246.40   $246.40  
  Purchase #4 $47.43   4.594%   $49.6089   $49.61   $49.60   $49.60  
  Purchase #5 $211.88   12.542%   $238.454   $238.45   $238.45   $238.50  
  Purchase #6 $18.50   7.855%   $19.9532   $19.95   $19.95   $20.00  
  Purchase #7 $245.81   3.234%   $253.7595   $253.76   $253.75   $253.80  
  7 purchase totals = $956.51       $1,025.5211   $1,025.52   $1,025.50   $1,025.70