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 $93.33   8.363%   $101.1352   $101.14   $101.15   $101.10  
  Purchase #2 $248.88   13.115%   $281.5206   $281.52   $281.50   $281.50  
  Purchase #3 $180.36   3.330%   $186.366   $186.37   $186.35   $186.40  
  Purchase #4 $94.98   3.595%   $98.3945   $98.39   $98.40   $98.40  
  Purchase #5 $5.75   6.267%   $6.1104   $6.11   $6.10   $6.10  
  Purchase #6 $164.33   13.509%   $186.5293   $186.53   $186.55   $186.50  
  Purchase #7 $210.81   10.277%   $232.4749   $232.47   $232.45   $232.50  
  7 purchase totals = $998.44       $1,092.5309   $1,092.53   $1,092.50   $1,092.50