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 $103.81   8.114%   $112.2331   $112.23   $112.25   $112.20  
  Purchase #2 $237.82   12.601%   $267.7877   $267.79   $267.80   $267.80  
  Purchase #3 $124.44   8.212%   $134.659   $134.66   $134.65   $134.70  
  Purchase #4 $9.91   9.355%   $10.8371   $10.84   $10.85   $10.80  
  Purchase #5 $242.48   3.725%   $251.5124   $251.51   $251.50   $251.50  
  Purchase #6 $238.52   3.114%   $245.9475   $245.95   $245.95   $245.90  
  Purchase #7 $33.43   6.156%   $35.488   $35.49   $35.50   $35.50  
  7 purchase totals = $990.41       $1,058.4648   $1,058.47   $1,058.50   $1,058.40