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 $219.53   10.843%   $243.3336   $243.33   $243.35   $243.30  
  Purchase #2 $7.53   13.297%   $8.5313   $8.53   $8.55   $8.50  
  Purchase #3 $62.44   8.499%   $67.7468   $67.75   $67.75   $67.70  
  Purchase #4 $117.69   7.267%   $126.2425   $126.24   $126.25   $126.20  
  Purchase #5 $173.30   11.337%   $192.947   $192.95   $192.95   $192.90  
  Purchase #6 $246.78   4.189%   $257.1176   $257.12   $257.10   $257.10  
  Purchase #7 $118.65   12.435%   $133.4041   $133.40   $133.40   $133.40  
  7 purchase totals = $945.92       $1,029.3229   $1,029.32   $1,029.35   $1,029.10