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 $125.32   6.385%   $133.3217   $133.32   $133.30   $133.30  
  Purchase #2 $158.30   7.179%   $169.6644   $169.66   $169.65   $169.70  
  Purchase #3 $52.87   7.475%   $56.822   $56.82   $56.80   $56.80  
  Purchase #4 $183.97   10.374%   $203.055   $203.06   $203.05   $203.10  
  Purchase #5 $120.64   12.760%   $136.0337   $136.03   $136.05   $136.00  
  Purchase #6 $154.96   3.845%   $160.9182   $160.92   $160.90   $160.90  
  Purchase #7 $156.33   6.334%   $166.2319   $166.23   $166.25   $166.20  
  7 purchase totals = $952.39       $1,026.0469   $1,026.04   $1,026.00   $1,026.00