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 $186.64   9.276%   $203.9527   $203.95   $203.95   $204.00  
  Purchase #2 $64.59   10.408%   $71.3125   $71.31   $71.30   $71.30  
  Purchase #3 $144.85   4.581%   $151.4856   $151.49   $151.50   $151.50  
  Purchase #4 $197.90   8.134%   $213.9972   $214.00   $214.00   $214.00  
  Purchase #5 $219.32   4.196%   $228.5227   $228.52   $228.50   $228.50  
  Purchase #6 $121.66   7.639%   $130.9536   $130.95   $130.95   $131.00  
  Purchase #7 $229.72   9.791%   $252.2119   $252.21   $252.20   $252.20  
  7 purchase totals = $1,164.68       $1,252.4362   $1,252.43   $1,252.40   $1,252.50