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 $178.82   13.828%   $203.5472   $203.55   $203.55   $203.50  
  Purchase #2 $89.81   3.196%   $92.6803   $92.68   $92.70   $92.70  
  Purchase #3 $247.82   13.787%   $281.9869   $281.99   $282.00   $282.00  
  Purchase #4 $104.44   6.425%   $111.1503   $111.15   $111.15   $111.20  
  Purchase #5 $167.84   8.267%   $181.7153   $181.72   $181.70   $181.70  
  Purchase #6 $32.40   12.487%   $36.4458   $36.45   $36.45   $36.40  
  Purchase #7 $244.86   6.183%   $259.9997   $260.00   $260.00   $260.00  
  7 purchase totals = $1,065.99       $1,167.5255   $1,167.54   $1,167.55   $1,167.50