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 $219.25   12.127%   $245.8384   $245.84   $245.85   $245.80  
  Purchase #2 $60.38   13.254%   $68.3828   $68.38   $68.40   $68.40  
  Purchase #3 $145.75   5.446%   $153.6875   $153.69   $153.70   $153.70  
  Purchase #4 $131.46   5.220%   $138.3222   $138.32   $138.30   $138.30  
  Purchase #5 $186.54   4.850%   $195.5872   $195.59   $195.60   $195.60  
  Purchase #6 $170.25   7.655%   $183.2826   $183.28   $183.30   $183.30  
  Purchase #7 $78.84   4.257%   $82.1962   $82.20   $82.20   $82.20  
  7 purchase totals = $992.47       $1,067.2969   $1,067.30   $1,067.35   $1,067.30