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 $160.74   7.535%   $172.8518   $172.85   $172.85   $172.90  
  Purchase #2 $147.89   11.203%   $164.4581   $164.46   $164.45   $164.50  
  Purchase #3 $137.83   6.639%   $146.9805   $146.98   $147.00   $147.00  
  Purchase #4 $220.73   12.487%   $248.2926   $248.29   $248.30   $248.30  
  Purchase #5 $216.87   10.288%   $239.1816   $239.18   $239.20   $239.20  
  Purchase #6 $47.44   4.818%   $49.7257   $49.73   $49.75   $49.70  
  Purchase #7 $99.78   4.324%   $104.0945   $104.09   $104.10   $104.10  
  7 purchase totals = $1,031.28       $1,125.5848   $1,125.58   $1,125.65   $1,125.70