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 $194.96   10.784%   $215.9845   $215.98   $216.00   $216.00  
  Purchase #2 $201.62   6.204%   $214.1285   $214.13   $214.15   $214.10  
  Purchase #3 $141.52   3.206%   $146.0571   $146.06   $146.05   $146.10  
  Purchase #4 $155.81   10.378%   $171.98   $171.98   $172.00   $172.00  
  Purchase #5 $244.32   12.623%   $275.1605   $275.16   $275.15   $275.20  
  Purchase #6 $22.37   9.293%   $24.4488   $24.45   $24.45   $24.40  
  Purchase #7 $161.35   8.654%   $175.3132   $175.31   $175.30   $175.30  
  7 purchase totals = $1,121.95       $1,223.0726   $1,223.07   $1,223.10   $1,223.10