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 $195.73   12.293%   $219.7911   $219.79   $219.80   $219.80  
  Purchase #2 $202.86   10.439%   $224.0366   $224.04   $224.05   $224.00  
  Purchase #3 $94.36   13.303%   $106.9127   $106.91   $106.90   $106.90  
  Purchase #4 $208.47   11.342%   $232.1147   $232.11   $232.10   $232.10  
  Purchase #5 $179.54   13.778%   $204.277   $204.28   $204.30   $204.30  
  Purchase #6 $34.53   12.845%   $38.9654   $38.97   $38.95   $39.00  
  Purchase #7 $66.28   6.361%   $70.4961   $70.50   $70.50   $70.50  
  7 purchase totals = $981.77       $1,096.5936   $1,096.60   $1,096.60   $1,096.60