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 $157.64   5.510%   $166.326   $166.33   $166.35   $166.30  
  Purchase #2 $101.56   9.249%   $110.9533   $110.95   $110.95   $111.00  
  Purchase #3 $150.81   7.637%   $162.3274   $162.33   $162.35   $162.30  
  Purchase #4 $60.84   4.826%   $63.7761   $63.78   $63.80   $63.80  
  Purchase #5 $187.25   7.737%   $201.7375   $201.74   $201.75   $201.70  
  Purchase #6 $159.55   9.848%   $175.2625   $175.26   $175.25   $175.30  
  Purchase #7 $7.92   8.414%   $8.5864   $8.59   $8.60   $8.60  
  7 purchase totals = $825.57       $888.9692   $888.98   $889.05   $889.00