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 $135.74   5.796%   $143.6075   $143.61   $143.60   $143.60  
  Purchase #2 $174.68   11.661%   $195.0494   $195.05   $195.05   $195.00  
  Purchase #3 $29.86   5.831%   $31.6011   $31.60   $31.60   $31.60  
  Purchase #4 $161.58   9.357%   $176.699   $176.70   $176.70   $176.70  
  Purchase #5 $246.95   5.310%   $260.063   $260.06   $260.05   $260.10  
  Purchase #6 $227.79   4.156%   $237.257   $237.26   $237.25   $237.30  
  Purchase #7 $95.98   13.861%   $109.2838   $109.28   $109.30   $109.30  
  7 purchase totals = $1,072.58       $1,153.5608   $1,153.56   $1,153.55   $1,153.60