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 $23.44   5.220%   $24.6636   $24.66   $24.65   $24.70  
  Purchase #2 $179.93   12.593%   $202.5886   $202.59   $202.60   $202.60  
  Purchase #3 $98.65   4.692%   $103.2787   $103.28   $103.30   $103.30  
  Purchase #4 $164.25   8.200%   $177.7185   $177.72   $177.70   $177.70  
  Purchase #5 $89.50   8.220%   $96.8569   $96.86   $96.85   $96.90  
  Purchase #6 $185.51   8.116%   $200.566   $200.57   $200.55   $200.60  
  Purchase #7 $199.68   12.746%   $225.1312   $225.13   $225.15   $225.10  
  7 purchase totals = $940.96       $1,030.8035   $1,030.81   $1,030.80   $1,030.90