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 $59.31   13.235%   $67.1597   $67.16   $67.15   $67.20  
  Purchase #2 $51.33   8.557%   $55.7223   $55.72   $55.70   $55.70  
  Purchase #3 $166.74   8.577%   $181.0413   $181.04   $181.05   $181.00  
  Purchase #4 $206.58   10.677%   $228.6365   $228.64   $228.65   $228.60  
  Purchase #5 $75.64   7.691%   $81.4575   $81.46   $81.45   $81.50  
  Purchase #6 $33.84   12.400%   $38.0362   $38.04   $38.05   $38.00  
  Purchase #7 $22.30   6.474%   $23.7437   $23.74   $23.75   $23.70  
  7 purchase totals = $615.74       $675.7972   $675.80   $675.80   $675.70