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 $81.94   12.786%   $92.4168   $92.42   $92.40   $92.40  
  Purchase #2 $144.56   9.247%   $157.9275   $157.93   $157.95   $157.90  
  Purchase #3 $192.48   3.798%   $199.7904   $199.79   $199.80   $199.80  
  Purchase #4 $169.65   6.109%   $180.0139   $180.01   $180.00   $180.00  
  Purchase #5 $132.96   4.375%   $138.777   $138.78   $138.80   $138.80  
  Purchase #6 $241.26   9.840%   $265   $265.00   $265.00   $265.00  
  Purchase #7 $114.70   4.120%   $119.4256   $119.43   $119.45   $119.40  
  7 purchase totals = $1,077.55       $1,153.3512   $1,153.36   $1,153.40   $1,153.30