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 $174.32   6.276%   $185.2603   $185.26   $185.25   $185.30  
  Purchase #2 $81.63   5.162%   $85.8437   $85.84   $85.85   $85.80  
  Purchase #3 $216.52   3.511%   $224.122   $224.12   $224.10   $224.10  
  Purchase #4 $174.39   11.634%   $194.6785   $194.68   $194.70   $194.70  
  Purchase #5 $75.86   12.324%   $85.209   $85.21   $85.20   $85.20  
  Purchase #6 $196.74   6.598%   $209.7209   $209.72   $209.70   $209.70  
  Purchase #7 $66.29   4.606%   $69.3433   $69.34   $69.35   $69.30  
  7 purchase totals = $985.75       $1,054.1777   $1,054.17   $1,054.15   $1,054.10