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 $159.48   10.230%   $175.7948   $175.79   $175.80   $175.80  
  Purchase #2 $50.51   4.111%   $52.5865   $52.59   $52.60   $52.60  
  Purchase #3 $169.75   7.111%   $181.8209   $181.82   $181.80   $181.80  
  Purchase #4 $178.30   5.237%   $187.6376   $187.64   $187.65   $187.60  
  Purchase #5 $44.36   7.872%   $47.852   $47.85   $47.85   $47.90  
  Purchase #6 $44.83   6.310%   $47.6588   $47.66   $47.65   $47.70  
  Purchase #7 $154.54   9.519%   $169.2507   $169.25   $169.25   $169.30  
  7 purchase totals = $801.77       $862.6013   $862.60   $862.60   $862.70