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 $238.30   11.773%   $266.3551   $266.36   $266.35   $266.40  
  Purchase #2 $186.93   8.763%   $203.3107   $203.31   $203.30   $203.30  
  Purchase #3 $22.84   12.751%   $25.7523   $25.75   $25.75   $25.80  
  Purchase #4 $157.76   11.742%   $176.2842   $176.28   $176.30   $176.30  
  Purchase #5 $235.29   7.811%   $253.6685   $253.67   $253.65   $253.70  
  Purchase #6 $216.25   4.573%   $226.1391   $226.14   $226.15   $226.10  
  Purchase #7 $15.33   7.131%   $16.4232   $16.42   $16.40   $16.40  
  7 purchase totals = $1,072.70       $1,167.9331   $1,167.93   $1,167.90   $1,168.00