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 $87.35   7.227%   $93.6628   $93.66   $93.65   $93.70  
  Purchase #2 $112.28   11.147%   $124.7959   $124.80   $124.80   $124.80  
  Purchase #3 $107.44   7.582%   $115.5861   $115.59   $115.60   $115.60  
  Purchase #4 $32.25   7.117%   $34.5452   $34.55   $34.55   $34.50  
  Purchase #5 $208.73   10.724%   $231.1142   $231.11   $231.10   $231.10  
  Purchase #6 $148.50   8.821%   $161.5992   $161.60   $161.60   $161.60  
  Purchase #7 $31.28   9.763%   $34.3339   $34.33   $34.35   $34.30  
  7 purchase totals = $727.83       $795.6373   $795.64   $795.65   $795.60