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 $233.80   10.369%   $258.0427   $258.04   $258.05   $258.00  
  Purchase #2 $119.58   10.537%   $132.1801   $132.18   $132.20   $132.20  
  Purchase #3 $161.46   12.415%   $181.5053   $181.51   $181.50   $181.50  
  Purchase #4 $192.68   9.797%   $211.5569   $211.56   $211.55   $211.60  
  Purchase #5 $103.26   8.480%   $112.0164   $112.02   $112.00   $112.00  
  Purchase #6 $118.41   13.476%   $134.3669   $134.37   $134.35   $134.40  
  Purchase #7 $25.89   3.632%   $26.8303   $26.83   $26.85   $26.80  
  7 purchase totals = $955.08       $1,056.4986   $1,056.51   $1,056.50   $1,056.50