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 $119.80   12.707%   $135.023   $135.02   $135.00   $135.00  
  Purchase #2 $163.66   5.113%   $172.0279   $172.03   $172.05   $172.00  
  Purchase #3 $93.31   13.634%   $106.0319   $106.03   $106.05   $106.00  
  Purchase #4 $202.81   7.778%   $218.5846   $218.58   $218.60   $218.60  
  Purchase #5 $63.32   12.613%   $71.3066   $71.31   $71.30   $71.30  
  Purchase #6 $107.94   13.390%   $122.3932   $122.39   $122.40   $122.40  
  Purchase #7 $156.37   10.797%   $173.2533   $173.25   $173.25   $173.30  
  7 purchase totals = $907.21       $998.6205   $998.61   $998.65   $998.60