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 $192.97   12.292%   $216.6899   $216.69   $216.70   $216.70  
  Purchase #2 $241.27   10.711%   $267.1124   $267.11   $267.10   $267.10  
  Purchase #3 $34.78   12.529%   $39.1376   $39.14   $39.15   $39.10  
  Purchase #4 $139.80   5.735%   $147.8175   $147.82   $147.80   $147.80  
  Purchase #5 $188.98   5.748%   $199.8426   $199.84   $199.85   $199.80  
  Purchase #6 $192.51   11.761%   $215.1511   $215.15   $215.15   $215.20  
  Purchase #7 $107.74   11.439%   $120.0644   $120.06   $120.05   $120.10  
  7 purchase totals = $1,098.05       $1,205.8155   $1,205.81   $1,205.80   $1,205.80