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 $144.47   8.449%   $156.6763   $156.68   $156.70   $156.70  
  Purchase #2 $229.82   12.829%   $259.3036   $259.30   $259.30   $259.30  
  Purchase #3 $115.89   4.477%   $121.0784   $121.08   $121.10   $121.10  
  Purchase #4 $130.36   9.459%   $142.6908   $142.69   $142.70   $142.70  
  Purchase #5 $180.60   3.370%   $186.6862   $186.69   $186.70   $186.70  
  Purchase #6 $164.92   8.182%   $178.4138   $178.41   $178.40   $178.40  
  Purchase #7 $13.58   10.637%   $15.0245   $15.02   $15.00   $15.00  
  7 purchase totals = $979.64       $1,059.8736   $1,059.87   $1,059.90   $1,059.90