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 $192.79   7.851%   $207.9259   $207.93   $207.95   $207.90  
  Purchase #2 $224.28   4.273%   $233.8635   $233.86   $233.85   $233.90  
  Purchase #3 $33.95   6.866%   $36.281   $36.28   $36.30   $36.30  
  Purchase #4 $180.57   12.858%   $203.7877   $203.79   $203.80   $203.80  
  Purchase #5 $137.75   6.210%   $146.3043   $146.30   $146.30   $146.30  
  Purchase #6 $184.65   13.768%   $210.0726   $210.07   $210.05   $210.10  
  Purchase #7 $203.32   12.628%   $228.9952   $229.00   $229.00   $229.00  
  7 purchase totals = $1,157.31       $1,267.2302   $1,267.23   $1,267.25   $1,267.30