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 $184.74   6.147%   $196.096   $196.10   $196.10   $196.10  
  Purchase #2 $240.35   10.221%   $264.9162   $264.92   $264.90   $264.90  
  Purchase #3 $23.80   7.775%   $25.6505   $25.65   $25.65   $25.70  
  Purchase #4 $165.58   10.471%   $182.9179   $182.92   $182.90   $182.90  
  Purchase #5 $57.34   6.122%   $60.8504   $60.85   $60.85   $60.90  
  Purchase #6 $185.82   10.485%   $205.3032   $205.30   $205.30   $205.30  
  Purchase #7 $185.68   6.610%   $197.9534   $197.95   $197.95   $198.00  
  7 purchase totals = $1,043.31       $1,133.6876   $1,133.69   $1,133.65   $1,133.80