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 $146.70   7.162%   $157.2067   $157.21   $157.20   $157.20  
  Purchase #2 $205.57   13.747%   $233.8297   $233.83   $233.85   $233.80  
  Purchase #3 $128.97   4.358%   $134.5905   $134.59   $134.60   $134.60  
  Purchase #4 $90.86   7.826%   $97.9707   $97.97   $97.95   $98.00  
  Purchase #5 $220.77   7.358%   $237.0143   $237.01   $237.00   $237.00  
  Purchase #6 $143.93   8.641%   $156.367   $156.37   $156.35   $156.40  
  Purchase #7 $38.91   7.494%   $41.8259   $41.83   $41.85   $41.80  
  7 purchase totals = $975.71       $1,058.8048   $1,058.81   $1,058.80   $1,058.80