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 $194.59   3.286%   $200.9842   $200.98   $201.00   $201.00  
  Purchase #2 $242.32   4.223%   $252.5532   $252.55   $252.55   $252.60  
  Purchase #3 $225.43   9.473%   $246.785   $246.79   $246.80   $246.80  
  Purchase #4 $77.69   8.651%   $84.411   $84.41   $84.40   $84.40  
  Purchase #5 $162.44   3.173%   $167.5942   $167.59   $167.60   $167.60  
  Purchase #6 $151.46   3.784%   $157.1912   $157.19   $157.20   $157.20  
  Purchase #7 $93.65   10.158%   $103.163   $103.16   $103.15   $103.20  
  7 purchase totals = $1,147.58       $1,212.6818   $1,212.67   $1,212.70   $1,212.80