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 $151.61   9.234%   $165.6097   $165.61   $165.60   $165.60  
  Purchase #2 $15.93   11.583%   $17.7752   $17.78   $17.80   $17.80  
  Purchase #3 $179.58   4.868%   $188.322   $188.32   $188.30   $188.30  
  Purchase #4 $192.87   4.628%   $201.796   $201.80   $201.80   $201.80  
  Purchase #5 $191.59   6.638%   $204.3077   $204.31   $204.30   $204.30  
  Purchase #6 $146.56   9.461%   $160.426   $160.43   $160.45   $160.40  
  Purchase #7 $23.90   4.774%   $25.041   $25.04   $25.05   $25.00  
  7 purchase totals = $902.04       $963.2776   $963.29   $963.30   $963.20