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 $91.48   7.466%   $98.3099   $98.31   $98.30   $98.30  
  Purchase #2 $178.60   13.634%   $202.9503   $202.95   $202.95   $203.00  
  Purchase #3 $35.40   4.244%   $36.9024   $36.90   $36.90   $36.90  
  Purchase #4 $238.56   13.253%   $270.1764   $270.18   $270.20   $270.20  
  Purchase #5 $242.35   9.854%   $266.2312   $266.23   $266.25   $266.20  
  Purchase #6 $239.83   12.604%   $270.0582   $270.06   $270.05   $270.10  
  Purchase #7 $200.42   11.158%   $222.7829   $222.78   $222.80   $222.80  
  7 purchase totals = $1,226.64       $1,367.4113   $1,367.41   $1,367.45   $1,367.50