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 $118.46   13.236%   $134.1394   $134.14   $134.15   $134.10  
  Purchase #2 $19.55   6.657%   $20.8514   $20.85   $20.85   $20.90  
  Purchase #3 $244.87   8.135%   $264.7902   $264.79   $264.80   $264.80  
  Purchase #4 $233.92   13.117%   $264.6033   $264.60   $264.60   $264.60  
  Purchase #5 $193.77   11.315%   $215.6951   $215.70   $215.70   $215.70  
  Purchase #6 $188.82   11.699%   $210.9101   $210.91   $210.90   $210.90  
  Purchase #7 $82.70   7.521%   $88.9199   $88.92   $88.90   $88.90  
  7 purchase totals = $1,082.09       $1,199.9094   $1,199.91   $1,199.90   $1,199.90