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 $164.33   11.539%   $183.292   $183.29   $183.30   $183.30  
  Purchase #2 $11.46   9.369%   $12.5337   $12.53   $12.55   $12.50  
  Purchase #3 $130.49   11.495%   $145.4898   $145.49   $145.50   $145.50  
  Purchase #4 $186.67   9.180%   $203.8063   $203.81   $203.80   $203.80  
  Purchase #5 $87.53   9.243%   $95.6204   $95.62   $95.60   $95.60  
  Purchase #6 $123.57   6.502%   $131.6045   $131.60   $131.60   $131.60  
  Purchase #7 $139.29   5.742%   $147.288   $147.29   $147.30   $147.30  
  7 purchase totals = $843.34       $919.6347   $919.63   $919.65   $919.60