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 $152.89   6.647%   $163.0526   $163.05   $163.05   $163.10  
  Purchase #2 $206.39   6.835%   $220.4968   $220.50   $220.50   $220.50  
  Purchase #3 $11.54   9.826%   $12.6739   $12.67   $12.65   $12.70  
  Purchase #4 $215.34   6.420%   $229.1648   $229.16   $229.15   $229.20  
  Purchase #5 $197.96   13.850%   $225.3775   $225.38   $225.40   $225.40  
  Purchase #6 $227.51   8.311%   $246.4184   $246.42   $246.40   $246.40  
  Purchase #7 $219.95   7.771%   $237.0423   $237.04   $237.05   $237.00  
  7 purchase totals = $1,231.58       $1,334.2263   $1,334.22   $1,334.20   $1,334.30