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 $164.48   11.578%   $183.5235   $183.52   $183.50   $183.50  
  Purchase #2 $152.70   9.545%   $167.2752   $167.28   $167.30   $167.30  
  Purchase #3 $217.94   10.573%   $240.9828   $240.98   $241.00   $241.00  
  Purchase #4 $67.93   7.266%   $72.8658   $72.87   $72.85   $72.90  
  Purchase #5 $247.40   4.147%   $257.6597   $257.66   $257.65   $257.70  
  Purchase #6 $73.47   5.540%   $77.5402   $77.54   $77.55   $77.50  
  Purchase #7 $31.49   11.732%   $35.1844   $35.18   $35.20   $35.20  
  7 purchase totals = $955.41       $1,035.0316   $1,035.03   $1,035.05   $1,035.10