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 $206.54   10.116%   $227.4336   $227.43   $227.45   $227.40  
  Purchase #2 $141.71   4.191%   $147.6491   $147.65   $147.65   $147.60  
  Purchase #3 $46.93   3.868%   $48.7453   $48.75   $48.75   $48.70  
  Purchase #4 $129.57   4.551%   $135.4667   $135.47   $135.45   $135.50  
  Purchase #5 $157.84   10.582%   $174.5426   $174.54   $174.55   $174.50  
  Purchase #6 $137.79   5.222%   $144.9854   $144.99   $145.00   $145.00  
  Purchase #7 $231.25   10.279%   $255.0202   $255.02   $255.00   $255.00  
  7 purchase totals = $1,051.63       $1,133.8429   $1,133.85   $1,133.85   $1,133.70