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 $199.55   5.392%   $210.3097   $210.31   $210.30   $210.30  
  Purchase #2 $99.29   3.638%   $102.9022   $102.90   $102.90   $102.90  
  Purchase #3 $124.67   8.467%   $135.2258   $135.23   $135.25   $135.20  
  Purchase #4 $159.29   8.227%   $172.3948   $172.39   $172.40   $172.40  
  Purchase #5 $99.36   10.385%   $109.6785   $109.68   $109.70   $109.70  
  Purchase #6 $186.65   8.175%   $201.9086   $201.91   $201.90   $201.90  
  Purchase #7 $73.83   11.684%   $82.4563   $82.46   $82.45   $82.50  
  7 purchase totals = $942.64       $1,014.8759   $1,014.88   $1,014.90   $1,014.90