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 $212.93   8.116%   $230.2114   $230.21   $230.20   $230.20  
  Purchase #2 $140.71   11.317%   $156.6342   $156.63   $156.65   $156.60  
  Purchase #3 $91.29   3.824%   $94.7809   $94.78   $94.80   $94.80  
  Purchase #4 $103.40   13.547%   $117.4076   $117.41   $117.40   $117.40  
  Purchase #5 $71.36   5.548%   $75.3191   $75.32   $75.30   $75.30  
  Purchase #6 $202.72   4.608%   $212.0613   $212.06   $212.05   $212.10  
  Purchase #7 $106.59   8.320%   $115.4583   $115.46   $115.45   $115.50  
  7 purchase totals = $929.00       $1,001.8728   $1,001.87   $1,001.85   $1,001.90