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 $82.25   12.635%   $92.6423   $92.64   $92.65   $92.60  
  Purchase #2 $242.42   7.536%   $260.6888   $260.69   $260.70   $260.70  
  Purchase #3 $201.72   7.741%   $217.3351   $217.34   $217.35   $217.30  
  Purchase #4 $196.35   7.757%   $211.5809   $211.58   $211.60   $211.60  
  Purchase #5 $146.40   5.740%   $154.8034   $154.80   $154.80   $154.80  
  Purchase #6 $61.32   9.450%   $67.1147   $67.11   $67.10   $67.10  
  Purchase #7 $50.27   4.722%   $52.6437   $52.64   $52.65   $52.60  
  7 purchase totals = $980.73       $1,056.8089   $1,056.80   $1,056.85   $1,056.70