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 $209.79   11.283%   $233.4606   $233.46   $233.45   $233.50  
  Purchase #2 $176.96   12.416%   $198.9314   $198.93   $198.95   $198.90  
  Purchase #3 $159.30   11.831%   $178.1468   $178.15   $178.15   $178.10  
  Purchase #4 $167.27   4.364%   $174.5697   $174.57   $174.55   $174.60  
  Purchase #5 $246.30   6.611%   $262.5829   $262.58   $262.60   $262.60  
  Purchase #6 $77.47   10.351%   $85.4889   $85.49   $85.50   $85.50  
  Purchase #7 $123.46   9.602%   $135.3146   $135.31   $135.30   $135.30  
  7 purchase totals = $1,160.55       $1,268.4949   $1,268.49   $1,268.50   $1,268.50