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 $197.64   4.249%   $206.0377   $206.04   $206.05   $206.00  
  Purchase #2 $172.61   12.716%   $194.5591   $194.56   $194.55   $194.60  
  Purchase #3 $29.74   13.720%   $33.8203   $33.82   $33.80   $33.80  
  Purchase #4 $67.84   11.259%   $75.4781   $75.48   $75.50   $75.50  
  Purchase #5 $62.49   5.481%   $65.9151   $65.92   $65.90   $65.90  
  Purchase #6 $224.35   7.444%   $241.0506   $241.05   $241.05   $241.10  
  Purchase #7 $35.64   5.191%   $37.4901   $37.49   $37.50   $37.50  
  7 purchase totals = $790.31       $854.3510   $854.36   $854.35   $854.40