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 $188.97   13.416%   $214.3222   $214.32   $214.30   $214.30  
  Purchase #2 $169.59   12.342%   $190.5208   $190.52   $190.50   $190.50  
  Purchase #3 $121.55   7.689%   $130.896   $130.90   $130.90   $130.90  
  Purchase #4 $190.76   7.203%   $204.5004   $204.50   $204.50   $204.50  
  Purchase #5 $229.46   7.736%   $247.211   $247.21   $247.20   $247.20  
  Purchase #6 $163.92   3.854%   $170.2375   $170.24   $170.25   $170.20  
  Purchase #7 $29.77   8.110%   $32.1843   $32.18   $32.20   $32.20  
  7 purchase totals = $1,094.02       $1,189.8722   $1,189.87   $1,189.85   $1,189.80