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 $52.76   13.479%   $59.8715   $59.87   $59.85   $59.90  
  Purchase #2 $12.98   10.406%   $14.3307   $14.33   $14.35   $14.30  
  Purchase #3 $167.87   4.716%   $175.7867   $175.79   $175.80   $175.80  
  Purchase #4 $200.46   9.183%   $218.8682   $218.87   $218.85   $218.90  
  Purchase #5 $232.37   5.733%   $245.6918   $245.69   $245.70   $245.70  
  Purchase #6 $34.45   4.121%   $35.8697   $35.87   $35.85   $35.90  
  Purchase #7 $99.54   8.653%   $108.1532   $108.15   $108.15   $108.20  
  7 purchase totals = $800.43       $858.5718   $858.57   $858.55   $858.70