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 $167.60   10.698%   $185.5298   $185.53   $185.55   $185.50  
  Purchase #2 $55.70   13.391%   $63.1588   $63.16   $63.15   $63.20  
  Purchase #3 $197.37   5.171%   $207.576   $207.58   $207.60   $207.60  
  Purchase #4 $173.93   12.668%   $195.9635   $195.96   $195.95   $196.00  
  Purchase #5 $185.39   8.851%   $201.7989   $201.80   $201.80   $201.80  
  Purchase #6 $110.39   12.588%   $124.2859   $124.29   $124.30   $124.30  
  Purchase #7 $18.32   10.335%   $20.2134   $20.21   $20.20   $20.20  
  7 purchase totals = $908.70       $998.5263   $998.53   $998.55   $998.60