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 $228.29   12.648%   $257.1641   $257.16   $257.15   $257.20  
  Purchase #2 $69.92   7.193%   $74.9493   $74.95   $74.95   $74.90  
  Purchase #3 $178.72   10.182%   $196.9173   $196.92   $196.90   $196.90  
  Purchase #4 $203.90   6.427%   $217.0047   $217.00   $217.00   $217.00  
  Purchase #5 $126.56   6.677%   $135.0104   $135.01   $135.00   $135.00  
  Purchase #6 $247.62   11.566%   $276.2597   $276.26   $276.25   $276.30  
  Purchase #7 $194.79   8.782%   $211.8965   $211.90   $211.90   $211.90  
  7 purchase totals = $1,249.80       $1,369.2020   $1,369.20   $1,369.15   $1,369.20