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 $183.74   8.653%   $199.639   $199.64   $199.65   $199.60  
  Purchase #2 $33.79   5.198%   $35.5464   $35.55   $35.55   $35.50  
  Purchase #3 $188.27   12.378%   $211.5741   $211.57   $211.55   $211.60  
  Purchase #4 $196.74   6.644%   $209.8114   $209.81   $209.80   $209.80  
  Purchase #5 $130.33   9.316%   $142.4715   $142.47   $142.45   $142.50  
  Purchase #6 $88.37   6.690%   $94.282   $94.28   $94.30   $94.30  
  Purchase #7 $219.31   3.293%   $226.5319   $226.53   $226.55   $226.50  
  7 purchase totals = $1,040.55       $1,119.8563   $1,119.85   $1,119.85   $1,119.80