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 $95.38   11.740%   $106.5776   $106.58   $106.60   $106.60  
  Purchase #2 $220.65   8.676%   $239.7936   $239.79   $239.80   $239.80  
  Purchase #3 $48.91   4.540%   $51.1305   $51.13   $51.15   $51.10  
  Purchase #4 $84.25   7.175%   $90.2949   $90.29   $90.30   $90.30  
  Purchase #5 $123.83   13.446%   $140.4802   $140.48   $140.50   $140.50  
  Purchase #6 $218.80   4.662%   $229.0005   $229.00   $229.00   $229.00  
  Purchase #7 $149.84   8.245%   $162.1943   $162.19   $162.20   $162.20  
  7 purchase totals = $941.66       $1,019.4716   $1,019.46   $1,019.55   $1,019.50