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 $160.91   11.367%   $179.2006   $179.20   $179.20   $179.20  
  Purchase #2 $247.94   5.282%   $261.0362   $261.04   $261.05   $261.00  
  Purchase #3 $89.92   7.691%   $96.8357   $96.84   $96.85   $96.80  
  Purchase #4 $190.66   7.278%   $204.5362   $204.54   $204.55   $204.50  
  Purchase #5 $95.31   11.582%   $106.3488   $106.35   $106.35   $106.30  
  Purchase #6 $225.74   12.660%   $254.3187   $254.32   $254.30   $254.30  
  Purchase #7 $221.48   10.470%   $244.669   $244.67   $244.65   $244.70  
  7 purchase totals = $1,231.96       $1,346.9452   $1,346.96   $1,346.95   $1,346.80