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 $61.28   13.771%   $69.7189   $69.72   $69.70   $69.70  
  Purchase #2 $134.93   11.141%   $149.9626   $149.96   $149.95   $150.00  
  Purchase #3 $7.62   10.400%   $8.4125   $8.41   $8.40   $8.40  
  Purchase #4 $82.93   13.492%   $94.1189   $94.12   $94.10   $94.10  
  Purchase #5 $171.61   11.613%   $191.5391   $191.54   $191.55   $191.50  
  Purchase #6 $127.36   10.859%   $141.19   $141.19   $141.20   $141.20  
  Purchase #7 $103.82   10.157%   $114.365   $114.37   $114.35   $114.40  
  7 purchase totals = $689.55       $769.3070   $769.31   $769.25   $769.30