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 $97.52   5.291%   $102.6798   $102.68   $102.70   $102.70  
  Purchase #2 $237.26   6.694%   $253.1422   $253.14   $253.15   $253.10  
  Purchase #3 $168.96   3.456%   $174.7993   $174.80   $174.80   $174.80  
  Purchase #4 $229.47   11.709%   $256.3386   $256.34   $256.35   $256.30  
  Purchase #5 $5.82   9.479%   $6.3717   $6.37   $6.35   $6.40  
  Purchase #6 $163.71   12.779%   $184.6305   $184.63   $184.65   $184.60  
  Purchase #7 $174.72   13.491%   $198.2915   $198.29   $198.30   $198.30  
  7 purchase totals = $1,077.46       $1,176.2536   $1,176.25   $1,176.30   $1,176.20