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 $233.48   12.471%   $262.5973   $262.60   $262.60   $262.60  
  Purchase #2 $188.95   7.152%   $202.4637   $202.46   $202.45   $202.50  
  Purchase #3 $137.51   13.666%   $156.3021   $156.30   $156.30   $156.30  
  Purchase #4 $250.37   8.868%   $272.5728   $272.57   $272.55   $272.60  
  Purchase #5 $64.49   7.765%   $69.4976   $69.50   $69.50   $69.50  
  Purchase #6 $99.26   10.857%   $110.0367   $110.04   $110.05   $110.00  
  Purchase #7 $91.44   4.273%   $95.3472   $95.35   $95.35   $95.30  
  7 purchase totals = $1,065.50       $1,168.8174   $1,168.82   $1,168.80   $1,168.80