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 $88.85   8.416%   $96.3276   $96.33   $96.35   $96.30  
  Purchase #2 $144.52   9.191%   $157.8028   $157.80   $157.80   $157.80  
  Purchase #3 $63.73   9.136%   $69.5524   $69.55   $69.55   $69.60  
  Purchase #4 $200.86   11.839%   $224.6398   $224.64   $224.65   $224.60  
  Purchase #5 $85.41   12.845%   $96.3809   $96.38   $96.40   $96.40  
  Purchase #6 $191.92   6.678%   $204.7364   $204.74   $204.75   $204.70  
  Purchase #7 $120.63   4.797%   $126.4166   $126.42   $126.40   $126.40  
  7 purchase totals = $895.92       $975.8565   $975.86   $975.90   $975.80